ISSUE
I recently ran into a problem trying to run a non-Steam game via proton where the game wouldn't start. It turns out, it was because the folder containing my game had white space. Replacing all the white space with underscores fixed the issue, but the steam client should be able to handle these types of file paths.

OS
Arch Linux

STEPS

1. Create a folder containing whitespace
   
   mkdir "My Game"
2. Create game.bat in "My Game"
   
   echo "hello world" > hello.txt
3. Add game.bat as a non-steam game
   
4. Click run

RESULTS
Program does not run.

EXPECTED
Program should launch, the file hello.txt should be created in "My Game".