This is what I would do, hopefully it will work for you
Back up the save manually or with ludusavi from discover in case steam cloud shits the bed,
remove the compatdata but double check the game id number (any of steamdb, steam store, protondb, get id from web address):
rm -r /home/deck/.steam/steam/steamapps/compatdata/1172620
(Or just navigate to the location and delete it with the file manager)
Set game to either to proton ge or just default if it's verified,
launch game.
I find this works whenever I screw up a game I'm modding or editing files of.
Edit: if that doesn't work try disabling steam cloud, backing up save, and deleting the non-backup version in case the save is broken and the game can't handle it.