Also I tried to patch it with the latest patch, broke it (I guess the patches are incremental?) and thus found out that RPGMaker MV really doesn’t like you trying to downgrade a game back to a previous version, even if you delete the old dir and extract it again, crashing with a Check failed: state.metadata.version() == GetCurrentDatabaseVersion() error. (Which btw broke this year’s record for esoteric errors, with a google query "Check failed: state.metadata.version()" returning one single result that wasn’t helpful.) Turns out it stores some db at ~/.config/KADOKAWA/RPGMV that needed to be purged.
Logging this here so that maybe my suffering can ease someone else’s.