you can check our directory structure here:

https://github.com/OpenTTD/OpenTTD/blob/master/docs/directory_structure.md

@ Eddi-z: Thanks. What should I've learnt there? The problem is not that it behaves differently for a reason (or without one). The problem is, that for a normal user it is not easy to see why it sudden behaves different and that it is somehow intended. Therefor a small hint "found savefiles in .config/save, but also found *.sav in ~/.local/share/openttd (likely due to respect of $XDG_DATA_HOME) - dismiss/remeber_dismissed" would be helpful. If you don't pay attention to the directory you're in when starting openttd -and who does all the time?- it appears as if your computer has lost the files. Scary experience.

Possibly related to the "portable app" behaviour: If openttd.cfg is found in the current directory during startup, portable mode is enabled and the search paths are different.

There have been several changes and fixes to how we look-up files and folders. I think this is mostly fixed (mainly due to #8357).

Note 1:
If you start OpenTTD from ~/.config/openttd while not having ~/.local/share/openttd/save already, it will create a save folder in ~/.config/openttd. This is as intended, as at that moment it considers the ~/.config/openttd to be a non-XDG folder. Basically, once you started OpenTTD from any other folder, things work as expected.

Note 2:
If for what-ever reason you create ~/.config/openttd/save, it will use ~/.config/openttd/save for your savegames when starting from ~/.config/openttd. This is because "working-directory" always wins from any other search-path. But a search-path never finds folders that don't exist.

Both notes are unlikely to ever happen in normal usage. So as long as you started the game once normally, you can now safely start it from ~/.config/openttd without it going all weird on you :)

If this isn't fixed for you, feel free to reopen :)