I reinstalled with the *.bin installer from the downloads page. (edit: but it reinstalled the old version.)
I have these JVMs installed and tried each:
temurin-8-jdk-amd64 (now asks for reinstall after reinstall; reinstalls old version; used to run fine with old version)
java-11-openjdk-amd64 (asks for reinstall after reinstall; reinstalls old version)
temurin-17-jdk-amd64 (doesn't start: Unrecognized VM option 'AggressiveOpts' in launcher.log)
java-21-openjdk-amd64 (doesn't start: Unrecognized VM option 'AggressiveOpts' in launcher.log)
AggressiveOpts is a CLI param btw.. AFAIK it was removed in Java 12.
I'll go to sleep now, but would be nice to get some feedback on what else to try or what JVM works.
// edit: Turns out the installer installs the old version and I changed this post accordingly a bit.
That's because it downloads the old version, at least in my case. Open "Options" in game and check the "About" tab. My version is 20260209004019, Bechamel's Expansion.