Thanks, sadly I had no luck again. The Linux version has the same behaviour as before. I searched a bit for Linux specific problems with RMMV and found this thread: https://www.reddit.com/r/RPGMaker/comments/dj3fnw/linux_problem/
So I downloaded the current version of nw.js, and indeed that got rid of the Fontconfig problems. However, in the window that opens I can only read "Failed to load: js/plugins/Community_Basic.js". Tried the Windows version in Wine again, also no luck, but it seems the messages are different. I can make out "Press F5 to restart the game", but that didn't help. Updating that version with the appropriate nw.js package made it worse since I didn't even get those messages.