Solved: Applying: [2021/05/01] Usage of raw option list on input line 252

All of a sudden running PdfLaTeX I get this error:

This is pdfTeX, Version 3.141592653-2.6-1.40.22 (TeX Live 2021) (preloaded format=pdflatex 2021.6.13)  15 JUN 2021 23:48
entering extended mode
 write18 enabled.
 %&-line parsing enabled.
**makeatletterdefcathedral@pagesize{a5}makeatothermakeatletter newcommand
{select@version}{version@final} makeatothernewififStatisticSelectedStatis
ticSelectedfalsenewififFinalSelectedFinalSelectedtruenewififDraftSelected
DraftSelectedfalsenewififKindleSelectedKindleSelectedfalseAtBeginDocument{
SetWatermarkText{}}input Een-halve-Surinamer-D.tex
 (./Een-halve-Surinamer-D.tex
(/zfs/texlive/2021/texmf-dist/tex/latex/koma-script/scrbook.cls
Document Class: scrbook 2021/03/17 v3.33 KOMA-Script document class (book)
(/zfs/texlive/2021/texmf-dist/tex/latex/koma-script/scrkbase.sty
Package: scrkbase 2021/03/17 v3.33 KOMA-Script package (KOMA-Script-dependent b
asics and keyval usage)

(/zfs/texlive/2021/texmf-dist/tex/latex/koma-script/scrbase.sty
Package: scrbase 2021/03/17 v3.33 KOMA-Script package (KOMA-Script-independent
basics and keyval usage)

(/zfs/texlive/2021/texmf-dist/tex/latex/koma-script/scrlfile.sty
Package: scrlfile 2021/03/17 v3.33 KOMA-Script package (file load hooks)

(/zfs/texlive/2021/texmf-dist/tex/latex/koma-script/scrlfile-hook.sty
Package: scrlfile-hook 2021/03/17 v3.33 KOMA-Script package (using LaTeX hooks)


(/zfs/texlive/2021/texmf-dist/tex/latex/koma-script/scrlogo.sty
Package: scrlogo 2021/03/17 v3.33 KOMA-Script package (logo)
)))
(/zfs/texlive/2021/texmf-dist/tex/latex/graphics/keyval.sty
Package: keyval 2014/10/28 v1.15 key=value parser (DPC)
KV@toks@=toks16
)
Applying: [2021/05/01] Usage of raw option list on input line 252.
Already applied: [0000/00/00] compatibility for LaTeX before 2021/05/01 on inpu
t line 337.

! Missing endcsname inserted.
<to be read again>
                   relax
l.580 FamilyProcessOptions{KOMA}
                                 relax

This is with TL2021. Wenn using TL2020 it compiles smoothly. Both TL updated.

Can somebody give me a hint in what direction to go to solve this (apart from just using TL2020)?

Here is the minimal example Ulrike asked for:

documentclass[%
iffalse% 
parskip=half,%
fi%
]{scrbook}
%
begin{document}
%
end{document}

This compiles on TL2020. and also on TL2021 when iffalse and fi are removed. As the example also compiles for class book, I think it is a bug in the KOMA class scrbook.