How to get alteration of biblatex-apa for online source

The example citation you give is more of a @report than an @online resource. Specifically, @report has the fields type and number for designators such as "Working Paper 2014/9".

Note that ctan is not particularly suitable as an example for these kind of entry types, since it does not have an author and is in fact much closer to a real @online entry than the NIDI paper.

With your setup you'll get

documentclass[ngerman, toc=listof, toc=bibliography, footnotes=multiple, numbers=noendperiod]{scrartcl}
usepackage[T1]{fontenc}
usepackage[utf8]{inputenc}
usepackage[ngerman]{babel}
usepackage[
backend=biber,
style=apa,
autocite=inline, 
natbib=true,
isbn=false,
doi=false,
eprint=false,
dashed=false,
pagetracker, 
ibidtracker=constrict
]{biblatex}

DeclareNameAlias{sortname}{family-given}
DeclareNameAlias{default}{given-family}
renewcommand*{newunitpunct}{addcommaspace}
renewcommand*{subtitlepunct}{addperiodspace}

DeclareDelimFormat{multinamedelim}{addslashspace}
DeclareDelimAlias{finalnamedelim}{multinamedelim}

renewbibmacro*{url+urldate}{%
    ifthenelse{iffieldundef{url}ORNOTiffieldundef{doi}}
    {}
    {iffieldundef{urlyear}
        {}
        {bibstring{retrieved}%
            setunit{addspace}%
            printtext{bibstring{from}}%
            setunit{addspace}}%
        iffieldundef{url}{}{printfield{url}renewcommand*{finentrypunct}{relax}}
        setunit*{addspace}%
        printurldate
        setunit{urldatecomma}%
}}

makeatletter
newbool{cbx:loccit}

DeclareBibliographyOption[boolean]{ibidpage}[true]{%
    ifstrequal{#1}{true}
    {ExecuteBibliographyOptions{loccittracker=constrict}}
    {ExecuteBibliographyOptions{loccittracker=false}}}

providecommand*{mkibid}[1]{#1}

newbibmacro*{cite:ibid}{%
  printtext[bibhyperref]{bibstring[mkibid]{ibidem}}%
  ifloccit
    {globalbooltrue{cbx:loccit}}
    {}}


renewbibmacro*{cite}{%
    globalboolfalse{cbx:loccit}%
    ifthenelse{ifciteibidANDNOTiffirstonpage}
    {usebibmacro{cite:ibid}}
    {iffieldequals{fullhash}{cbx@lasthash}
        % Multiple cites in one command
        {setunit{compcitedelim}%
            usebibmacro{cite:plabelyear+extradate}}%
        % Single cite
        {ifnameundef{labelname}
            % No author/editor
            {usebibmacro{cite:noname}%
                setunit{printdelim{nameyeardelim}}%
                usebibmacro{cite:plabelyear+extradate}%
                savefield{fullhash}{cbx@lasthash}}
            % Normal cite
            {ifnameundef{shortauthor}
                {printnames{labelname}}%
                {cbx@apa@ifnamesaved
                    {printnames{shortauthor}}
                    {ifnameundef{groupauthor}
                        {printnames[labelname]{author}}
                        {printnames[labelname]{groupauthor}}%
                        addspaceprintnames[sabrackets]{shortauthor}}}%
                setunit{printdelim{nameyeardelim}}%
                usebibmacro{cite:plabelyear+extradate}%
                savefield{fullhash}{cbx@lasthash}}}%
        setunit{multicitedelim}}}

renewbibmacro*{textcite}{%
    globalboolfalse{cbx:loccit}%
    iffieldequals{fullhash}{cbx@lasthash}
    % Compact cite - more than one thing for same author
    {setunit{compcitedelim}%
        usebibmacro{cite:plabelyear+extradate}}
    % New cite
    {ifbool{cbx:parens}
        {bibcloseparenglobalboolfalse{cbx:parens}}
        {}%
        setunit{textcitedelim}%
        ifnameundef{labelname}
        % No author/editor
        {iffieldundef{shorthand}%
            % Cite using title
            {usebibmacro{cite:noname}%
                setunit{globalbooltrue{cbx:parens}addspacebibopenparen}%
                usebibmacro{cite:plabelyear+extradate}}
            % Cite using shorthand
            {usebibmacro{cite:shorthand}}}
        % Normal cite with author/editor
        % Normal full cite
        {ifnameundef{shortauthor}%
            % Normal full cite
            {printnames{labelname}}
            % Cite using short author
            {cbx@apa@ifnamesaved
                {printnames{shortauthor}}
                {ifnameundef{groupauthor}
                    {printnames[labelname]{author}}
                    {printnames[labelname]{groupauthor}}}}%
            % Year
            setunit{globalbooltrue{cbx:parens}addspacebibopenparen}%
            % Put the shortauthor inside the year brackets if necessary
            ifnameundef{shortauthor}
            {}
            {cbx@apa@ifnamesaved
                {}
                {printnames{shortauthor}%
                    setunit{printdelim{nameyeardelim}}}}%
            % Print prenote (belongs to first cite)
            ifnumequal{value{citecount}}{1}
            {usebibmacro{prenote}}
            {}%
            % Actual year printing
            ifthenelse{ifciteibidANDNOTiffirstonpage}
            {usebibmacro{cite:ibid}}
            {usebibmacro{cite:plabelyear+extradate}}%
            % Save name hash for checks later
            savefield{fullhash}{cbx@lasthash}}%
        stepcounter{textcitecount}}}

letbibmacro{orig:postnote}{postnote}

renewbibmacro*{postnote}{%
    ifbool{cbx:loccit}
    {}
    {usebibmacro{orig:postnote}}}
makeatother
ExecuteBibliographyOptions{ibidpage=true}

DeclareSourcemap{
    maps[datatype=bibtex]{
        map{
            step[fieldsource=urldate, match=regexp{A(d{2}).(d{2}).(d{4})Z}, replace={$3-$2-$1}]
        }
    }
}

DeclareStyleSourcemap{
    maps[datatype=bibtex, overwrite=true]{
        map{
            step[fieldsource=url, final]
            step[typesource=misc, typetarget=online]
        }
    }
}

begin{filecontents}{jobname.bib}
@report{kristiansen,
  author       = {Marcus H. Kristiansen},
  title        = {Agency as an Empirical Concept},
  subtitle     = {An Assessment of Theory and Operationalization},
  date         = {2014},
  type         = {Working Paper},
  number       = {2014/9},
  location     = {Den Haag},
  publisher    = {NIDI},
  url          = {https://www.nidi.nl/shared/content/output/papers/nidi-wp-2014-09.pdf},
  urldate      = {2020-07-28},
}
end{filecontents}
addbibresource{jobname.bib}
addbibresource{biblatex-examples.bib}

begin{document}
  Lorem ipsum. autocite{kristiansen}
    
  printbibliography
end{document}

which isn't quite what you show in the picture, but comes close.

I note, though, that your picture includes the location, which is not usually done in the 7th edition of APA style, which biblatex-apa implements. And indeed if I switch to biblatex-apa6 for 6th edition APA style I get something much closer to what you need.

documentclass[ngerman, toc=listof, toc=bibliography, footnotes=multiple, numbers=noendperiod]{scrartcl}
usepackage[T1]{fontenc}
usepackage[utf8]{inputenc}
usepackage[ngerman]{babel}
usepackage[backend=biber,
  style=apa6]{biblatex}

begin{filecontents}{jobname.bib}
@report{kristiansen,
  author       = {Marcus H. Kristiansen},
  title        = {Agency as an Empirical Concept},
  subtitle     = {An Assessment of Theory and Operationalization},
  date         = {2014},
  type         = {Working Paper},
  number       = {2014/9},
  location     = {Den Haag},
  publisher    = {NIDI},
  url          = {https://www.nidi.nl/shared/content/output/papers/nidi-wp-2014-09.pdf},
  urldate      = {2020-07-28},
}
end{filecontents}
addbibresource{jobname.bib}

begin{document}
  Lorem ipsum. autocite{kristiansen}
    
  printbibliography
end{document}