Current release day version of the game has many minor bugs and issues that I believe are not Proton specific:

• Mouse/controller settings do not apply during gameplay, have to exit to main menu.
• The sensitivity settings sometimes resets during gameplay.
• Some chapters of the game crash if pausing the game.
• A couple of common resolutions like 2560x1440 are missing in the options.

Out of the box the game also had flickering shadows on my system, that coluld be fixed using the launch option mentioned above. Alternatively one can use launch option "-dx11" instead to force the game to use DX11.