lualatex no longer working

For some reason lualatex is running mktexfmt lualatex.fmt (as user then), which creates ~/.texlive2021/texmf-var/web2c/luahbtex/lualatex.fmt. There already is /usr/share/texmf-var/web2c/luahbtex/lualatex.fmt generated from the texlive trigger that seems to be valid. And lualatex even after creating a new lualatex.fmt is still not yet pleased with the result and will recreate it on each subsequent start, so it never actually generates a document.

I have just started to track the bug down, but I thought I might document it here in case someone else also steps into it. The issue is not fixed by !32673 (merged) :/