Thank you, glad you’re enjoying the game! :D
I don’t have a Linux machine to test on at the moment, but, looking at the code, it looks like the save file directory is $XDG_DATA_HOME/Leone Gaming/Upheaval, which looks like it’s possibly equivalent to $HOME/.local/share/Leone Gaming/Upheaval. Let me know if that works for you!
Also, let me know if you have any issues on the Steam Deck. I don’t have one to test on yet, but I’d love to make it a better experience for players if I can. :) Thanks!! I appreciate you!