I created a directory called DeadByDaylight, as it was missing, and changed the settings "Wine prefix directory" of DbD to that directory.
Running the game with Proton GE shows multiple windows-styled message boxes "File not located" or something like that.
However
Then I switched back to Wine. Again - Unexpected error #1
After that, I switched back again to Proton GE. For some reason this time the game launched correctly.
I'll try to play for some time, to be sure everything works correctly, but, I have no idea why, the issue has been resolved.
Give me some time to make sure everything is in order, then I'll mark as solved. Thank You very much