how to insert keys from token list in command

When i try to insert in command variable with keys,i get an error:

LaTeX3 Error: The key ‘__tag/mc/g__last_mc_tl’ is unknown and is being
(LaTeX3) ignored.

I understand, why this happen. It hapen because according to expl3 documentation,l3keys convert argument as string,so instead of variable,i give variable name. But i haven’t any idea,how to fix it. Thanks everybody very much for the help.

RequirePackage[patches]{pdfresources}
DeclareDocumentMetadata{pdfversion=2.0}
documentclass{article}
usepackage{tagpdf}
tagpdfsetup{tabsorder=structure,uncompress,activate-all,add-new-tag=Title/P,interwordspace=true}
begin{document}
tagstructbegin{tag=Document}
tagstructbegin{tag=P}
ExplSyntaxOn
  tl_new:N g__mc_tl
tl_gset:Nn g__mc_tl{tag=P,actualtext=test of paragraph}
tagstructbegin{tag=P}
tagmcbegin{g__last_mc_tl}
Test
tagmcend
tagstructend
ExplSyntaxOff
tagstructend
end{document}=