I encountered a problem with Project Zomboid and the CleanHotBar mod on Linux where it simply wouldn't launch. I asked ChatGPT, and it turned out that possibly after a Java/JVM update or a mod update, something happened with the encoding. It needs to be set in the game properties: -Dfile.encoding=UTF-8.

Alternatively, in the JVM:
export LANG=en_US.UTF-8
export LC_ALL=en_US.UTF-8
(Be careful when setting the encoding in the JVM, as it might break your system.)

This might help you if you have problems with other UI mods that change the game's interface. And a piece of advice: read the log files (console.txt and others) carefully.