Shortcut for $ ^{prime} $ is not working in beamer

I am preparing some lecture notes in beamer documentclass. After I added quite a much of customisations, I realised that the shortcut ' for $ ^{prime} $ is not working. How do I restore the usual behaviour? Following is an MWE. Please help.

documentclass[aspectratio=169,10pt, notheorems]{beamer}
setbeamerfont{headline}{size=fontsize{8}{0}selectfont}
setbeamerfont{footline}{size=fontsize{6}{0}selectfont}
usetheme{CambridgeUS}
usefonttheme{serif}
usepackage{xcolor}
definecolor{sapphire}{rgb}{0.01, 0.01, 1}
setbeamertemplate{enumerate subitem}{(alph{enumii})}
setbeamertemplate{enumerate item}{arabic{enumi}.}
setbeamertemplate{bibliography item}{insertbiblabel}
%setbeamertemplate{theorems}[numbered]
usepackage{hanging}% http://ctan.org/pkg/hanging
setbeamertemplate{footnote}{%
    hangpara{2em}{1}%
    makebox[2em][l]{insertfootnotemark}footnotesizeinsertfootnotetextpar%
}

usepackage{ifthen}
usepackage{wrapfig}

setbeamertemplate{navigation symbols}{}
setbeamercolor{background canvas}{bg=black}
setbeamercolor{normal text}{fg=white}

setbeamercolor{structure}{fg=magenta}
setbeamercolor{structure}{bg=black}

%usepackage{enumitem}
usepackage{mathtools, amssymb, amsfonts, amsthm, amsmath}
usepackage{stmaryrd}
usepackage{nccmath}
usepackage{graphicx}
usepackage{ragged2e}
%usepackage{latex2e}
usepackage{tikz}
usepackage{pgfplots}
usetikzlibrary{hobby}
usetikzlibrary{decorations.pathreplacing, calligraphy}
usetikzlibrary{decorations.markings}
usetikzlibrary{patterns}
usepackage{etoolbox}
usepackage[mathscr]{eucal}
usepackage{upgreek}


newtagform{dots}{$ cdots $(}{)}
usetagform{dots}


usepackage{caption}
usepackage[labelformat=simple, labelsep=colon]{subcaption}
setbeamertemplate{caption}[numbered]
renewcommand{thesubfigure}{thefigure.(alph{subfigure})}
makeatletter
renewcommandp@subfigure{}
makeatother


makeatletter
letsave@mathaccentmathaccent
newcommand*if@single[3]{%
    setbox0hbox{${mathaccent"0362{#1}}^H$}%
    setbox2hbox{${mathaccent"0362{kern0pt#1}}^H$}%
    ifdimht0=ht2 #3else #2fi
}
%The bar will be moved to the right by a half of macc@kerna, which is computed by amsmath:
newcommand*rel@kern[1]{kern#1dimexprmacc@kerna}
%If there's a superscript following the bar, then no negative kern may follow the bar;
%an additional {} makes sure that the superscript is high enough in this case:
newcommand*widebar[1]{@ifnextchar^{{wide@bar{#1}{0}}}{wide@bar{#1}{1}}}
%Use a separate algorithm for single symbols:
newcommand*wide@bar[2]{if@single{#1}{wide@bar@{#1}{#2}{1}}{wide@bar@{#1}{#2}{2}}}
newcommand*wide@bar@[3]{%
    begingroup
    defmathaccent##1##2{%
        %Enable nesting of accents:
        letmathaccentsave@mathaccent
        %If there's more than a single symbol, use the first character instead (see below):
        if#32 letmacc@nucleusfirst@char fi
        %Determine the italic correction:
        setboxz@hbox{$macc@style{macc@nucleus}_{}$}%
        setboxtw@hbox{$macc@style{macc@nucleus}{}_{}$}%
        dimen@wdtw@
        advancedimen@-wdz@
        %Now dimen@ is the italic correction of the symbol.
        dividedimen@ 3
        @tempdimawdtw@
        advance@tempdima-scriptspace
        %Now @tempdima is the width of the symbol.
        divide@tempdima 10
        advancedimen@-@tempdima
        %Now dimen@ = (italic correction / 3) - (Breite / 10)
        ifdimdimen@>z@ dimen@0ptfi
        %The bar will be shortened in the case dimen@<0 !
        rel@kern{0.6}kern-dimen@
        if#31
        overline{rel@kern{-0.6}kerndimen@macc@nucleusrel@kern{0.4}kerndimen@}%
        [email protected]@kerna
        %Place the combined final kern (-dimen@) if it is >0 or if a superscript follows:
        letfinal@kern#2%
        ifdimdimen@<z@ letfinal@kern1fi
        iffinal@kern1 kern-dimen@fi
        else
        overline{rel@kern{-0.6}kerndimen@#1}%
        fi
    }%
    macc@depth@ne
    letmath@bgroup@empty letmath@egroupmacc@set@skewchar
    mathsurroundz@ frozen@everymath{mathgroupmacc@grouprelax}%
    macc@set@skewcharrelax
    letmathaccentVmacc@nested@a
    %The following initialises macc@kerna and calls mathaccent:
    if#31
    macc@nested@arelax111{#1}%
    else
    %If the argument consists of more than one symbol, and if the first token is
    %a letter, use that letter for the computations:
    defgobble@till@marker##1endmarker{}%
    futureletfirst@chargobble@till@marker#1endmarker
    ifcatnoexpandfirst@char Aelse
    deffirst@char{}%
    fi
    macc@nested@arelax111{first@char}%
    fi
    endgroup
}
makeatother


newcommand{R}{mathbb{R}}
newcommand{N}{mathbb{N}}
newcommand{Q}{mathbb{Q}}
newcommand{Z}{mathbb{Z}}
newcommand{C}{mathbb{C}}
renewcommand{l}{lambda}
renewcommand{L}{Lambda}
newcommand{G}{mathscr{G}}
newcommand{B}{mathscr{B}}
renewcommand{d}{delta}
newcommand{e}{epsilon}
renewcommand{a}{alpha}
renewcommand{b}{beta}
renewcommand{r}{mathrm{r}}
newcommand{n}{mathrm{N}}
newcommand{g}{gamma}
renewcommand{th}{uptheta}
letemptysetvarnothing
renewcommand{qedsymbol}{$blacksquare$}
newcommand{abs}[1]{leftlvert #1 rightrvert}
newcommand{ts}{textstyle}
newcommand{func}[3]{#1mathpunct{:}#2to#3}
newcommand{mat}[1]{leftllbracket #1 rightrrbracket}
newcommand{scr}[1]{mathscr{#1}}
DeclareMathOperator{image}{Im}
newcommand{comb}[2]{begin{psmallmatrix}#1  #2end{psmallmatrix}}
renewcommand{limsup}{widebar{lim},}
renewcommand{liminf}{underline{lim},}

%usepackage[symbol]{footmisc}
%renewcommand{thefootnote}{fnsymbol{footnote}}


setbeamercolor{block title}{use=structure}
setbeamercolor{block body}{parent=normal text,use=block title,fg=yellow,bg=black}

makeatletter
newenvironment<>{proofs}[1][proofname]{pardefinsertproofname{scshape #1@addpunct{:}}usebeamertemplate{proof begin}#2} {usebeamertemplate{proof end}}

newenvironment<>{proofc}{setbeamertemplate{proof begin}{begin{block}{}}parusebeamertemplate{proof begin}}  {usebeamertemplate{proof end}}

newenvironment<>{proofe}{parpushQED{qed}setbeamertemplate{proof begin}{begin{block}{}}usebeamertemplate{proof begin}}        {popQEDusebeamertemplate{proof end}}
makeatother
        
makeatletter
renewenvironment<>{proof}[1][proofname]
{
    par
    definsertproofname{scshape #1@addpunct{:}}%
    usebeamertemplate{proof begin}#2
    parskip 1ex
    pushQED{qed}
}
{
    popQEDusebeamertemplate{proof end}
}
makeatother
        
        
setbeamertemplate{blocks}[rounded][shadow=false]

        


%setbeamercolor{block title proofs}{use=structure}
%setbeamercolor{block body proofs}{parent=normal text,use=block title proof,fg=yellow,bg=black}
%
%setbeamercolor{block title proofc}{use=structure}
%setbeamercolor{block body proofc}{parent=normal text,use=block title proof,fg=yellow,bg=black}
%
%setbeamercolor{block title proofe}{use=structure}
%setbeamercolor{block body proofe}{parent=normal text,use=block title proof,fg=yellow,bg=black}



BeforeBeginEnvironment{theorem}{
    setbeamercolor{block title}{use=structure,fg=structure.fg,bg=pink!50!white}
    setbeamercolor{block body}{fg=black, bg=pink!25!white}
}
AfterEndEnvironment{theorem}{
    setbeamercolor{block title}{use=structure,fg=structure.fg,bg=structure.fg!20!bg}
    setbeamercolor{block body}{parent=normal text,use=block title,bg=block title.bg!50!bg, fg=black}
}

BeforeBeginEnvironment{proposition}{
    setbeamercolor{block title}{use=structure,fg=structure.fg,bg=pink!40!white}
    setbeamercolor{block body}{fg=black, bg=pink!15!white}
}
AfterEndEnvironment{proposition}{
    setbeamercolor{block title}{use=structure,fg=structure.fg,bg=structure.fg!20!bg}
    setbeamercolor{block body}{parent=normal text,use=block title,bg=block title.bg!50!bg, fg=black}
}

BeforeBeginEnvironment{corollary}{
    setbeamercolor{block title}{use=structure,fg=structure.fg,bg=pink!30!white}
    setbeamercolor{block body}{fg=black, bg=pink!5!white}
}
AfterEndEnvironment{corollary}{
    setbeamercolor{block title}{use=structure,fg=structure.fg,bg=structure.fg!20!bg}
    setbeamercolor{block body}{parent=normal text,use=block title,bg=block title.bg!50!bg, fg=black}
}

BeforeBeginEnvironment{lemma}{
    setbeamercolor{block title}{use=structure,fg=structure.fg,bg=pink!30!white}
    setbeamercolor{block body}{fg=black, bg=pink!5!white}
}
AfterEndEnvironment{lemma}{
    setbeamercolor{block title}{use=structure,fg=structure.fg,bg=structure.fg!20!bg}
    setbeamercolor{block body}{parent=normal text,use=block title,bg=block title.bg!50!bg, fg=black}
}


BeforeBeginEnvironment{definition}{%
    setbeamercolor{block title}{fg=red!75!black,bg=olive!40!white}
    setbeamercolor{block body}{fg=black, bg=olive!20!white}
}
AfterEndEnvironment{definition}{
    setbeamercolor{block title}{use=structure,fg=structure.fg,bg=structure.fg!20!bg}
    setbeamercolor{block body}{parent=normal text,use=block title,bg=block title.bg!50!bg, fg=black}
}

%%setbeamercolor{background canvas}{bg=black}
%setbeamercolor{proofs}{fg=black}
%setbeamercolor{proofc}{fg=black}
%setbeamercolor{proofe}{fg=black}
%setbeamerfont{framesubtitle}{size=large,font=scshape}
        
%setbeamertemplate{theorem}[ams style]
%setbeamertemplate{figures}[numbered]
        
setbeamertemplate{theorem}[ams style]
setbeamertemplate{theorems}[numbered]

makeatletter
ifbeamer@countsect
newtheorem{theorem}{translate{Theorem}}[section]
else
newtheorem{theorem}{translate{Theorem}}[section]
fi
newtheorem{corollary}{translate{Corollary}}[theorem]
newtheorem{lemma}[theorem]{translate{Lemma}}
newtheorem{proposition}[theorem]{translate{Proposition}}
newtheorem{problem}{translate{Problem}}
newtheorem{solution}{translate{Solution}}

theoremstyle{definition}
newtheorem{definition}[theorem]{translate{Definition}}
newtheorem{definitions}[theorem]{translate{Definitions}}


newtheorem*{exc}{translate{Exercise}}
newtheorem*{excs}{translate{Exercises}}


newenvironment{lem}{begin{lemma}}{end{lemma}}
newenvironment{thm}{begin{theorem}}{end{theorem}}
newenvironment{cor}{begin{corollary}}{end{corollary}}
newenvironment{defn}{begin{definition}}{end{definition}}
newenvironment{prop}{begin{proposition}}{end{proposition}}
makeatother


makeatletter
defth@myexmpstyle{%
    small % body font
    setbeamercolor{block title}{use=structure,fg=magenta,bg=black}
    setbeamercolor{block body}{fg=lime,bg=black}
    definserttheoremblockenv{block}
}
makeatother
theoremstyle{myexmpstyle}
newtheorem*{example}{translate{Example:}}
newtheorem*{examples}{translate{Examples:}}



makeatletter
defth@mystyle{%
    normalfont % body font
    setbeamercolor{block title}{use=structure}
    setbeamercolor{block body}{bg=black, fg=cyan!40!white}
    definserttheoremblockenv{block}
}
makeatother
theoremstyle{mystyle}
newtheorem*{Rem}{Remark:}
newtheorem*{rems}{Remarks:}

newenvironment*{Exmps}
{
    begin{examples}parskip 1ex
        vspace{-1ex}footnotesize
        begin{enumerate}%[label=arabic*.]
        }
        {
        end{enumerate}normalsize
    end{examples}  
}

newenvironment*{exercises}
{
    footnotesize
    begin{excs}
        vspace{-1ex}
        begin{enumerate}%[label=arabic*.]
        }
        {
        end{enumerate}
    end{excs}
    normalsize
}

newenvironment*{exmp}{begin{example}parskip 1ex footnotesize}{end{example}normalsize}
newenvironment*{exercise}{begin{exc}footnotesize}{end{exc}normalsize}


newenvironment{rem}{begin{Rem}parskip 1ex vspace{-2ex}footnotesize}{end{Rem}normalsize}

newenvironment{Rems}
{
    
    begin{rems}
        vspace{-1ex}footnotesize
        begin{enumerate}%[label=(alph*)]
        }
        {
        end{enumerate}normalsize
    end{rems}  
}

%usepackage{varioref}
usepackage{hyperref}
hypersetup
{
    colorlinks=true, %set true if you want colored links
    %   linktoc=all,     %set to all if you want both sections and subsections linked
    linkcolor=black,  %choose some color if you want links to stand out
    citecolor=teal,
}
usepackage{cleveref}
crefname{prop}{proposition}{propositions}
crefname{proposition}{proposition}{propositions}

crefname{lemma}{lemma}{lemmas}
crefname{lem}{lemma}{lemmas}
crefname{figure}{figure}{figures}
%newcommand{myref}[1]{beamergotobutton{cref{#1}}}
newcommand{link}[2]{hyperlink{#1}{beamerbutton{#2}}}
%       newcommand{Label}[1]{hypertarget<.>{label#1}{}}


bibliographystyle{amsalpha}


apptocmd{frame}{}{justifying}{}
parskip 1ex
%
%
%
begin{document}
    
    makeatletter
    defstringpleasehidethistitle{{please hide this titleifnumbeamer@autobreakcount>0relax{}spaceusebeamertemplate*{frametitle continuation}fi}}
    defbeamertemplate*{frametitle}{only sub}[1][left]
    {
        ifbeamercolorempty[bg]{frametitle}{}{nointerlineskip}%
        @tempdima=textwidth%
        advance@tempdima bybeamer@leftmargin%
        advance@tempdima bybeamer@rightmargin%
        begin{beamercolorbox}[sep=0.3cm,#1,wd=the@tempdima]{frametitle}
            usebeamerfont{frametitle}%
            vbox{}vskip-1ex%
            if@tempswaelsecsname beamer@fte#1endcsnamefi%
            ifxinsertframetitlestringpleasehidethistitle%   check if magic word presents
            else%                                             check if magic word presents
            strutinsertframetitlestrutpar%               check if magic word presents
            fi%                                               check if magic word presents
            {%
                ifxinsertframesubtitle@empty%
                else%
                {usebeamerfont{framesubtitle}usebeamercolor[fg]{framesubtitle}insertframesubtitlestrutpar}%
                fi
            }%
            vskip-1ex%
            [email protected]% set inside beamercolorbox... evil here...
        end{beamercolorbox}%
    }
    
    begin{frame}
        $ a^{prime} $ % WORKS!
        $ a' $ % DOES NOT WORK!
    end{frame}
end{document}