I recently encountered problem with seminar class. I am using app-text/texlive-2021 on Gentoo Linux.
Simple test case:
\documentclass{seminar}
\begin{document}
\end{document}
Output:
pet@pvn ~/Documents/work $ pdflatex pokus.tex
This is pdfTeX, Version 3.141592653-2.6-1.40.22 (TeX Live 2021 Gentoo Linux) (preloaded format=pdflatex)
restricted \write18 enabled.
entering extended mode
(./pokus.tex
LaTeX2e <2020-10-01> patch level 4
L3 programming layer <2021-02-18>
(/usr/share/texmf-dist/tex/latex/seminar/seminar.cls
Document Class: seminar 2014/01/17, 1.61
Documentclass: `seminar' v1.61 <2014/01/17> (tvz,hv)
...
(/usr/share/texmf-dist/tex/latex/seminar/sem-page.sty))
! Extra \endgroup.
\document ->\endgroup
\the \before@document \begingroup \UseOneTimeHook {beg...
l.3 \begin{document}
?
Any hint? Thank you.