I was facing an issue for the last few months where none of my games were launching on Proton 9.0-4 every game had the same symptoms, the game would launch and you could only hear music, the screen was black or stuck on a single frame or it only loaded the game’s mouse cursor and nothing else.
So here’s the solution (this is an Nvidia issue it seems):
In terminal type: sudo nvidia-settings and enter your password
The Nvidia settings GUI config window should open up
Then do the following:
- X Server Display Configuration
- Advanced
- de-select “Force Composition Pipeline” and “Force Full Composition Pipeline” (these used to be needed for screen tearing but it’s not required any more)
- Click “Apply”
- Click “Save to X Configuration File”: /etc/X11/nvidia.conf (note: in Manjaro the correct path is “/etc/X11/mhwd.d/nvidia.conf” you can click on browse to go to the right directory/file)
- Click “save” if the path is correct
- Quit (when you quit it says you have pending changes - X Server Display Configuration - Apply - if you’ve clicked apply in the steps above then you can just quit and it will save your changes)
No need to restart. Now all the games launch and work perfectly fine after doing this… I tested SteamWorld Heist II, Ravenswatch, Punch Club 2 and Dark Quest 3… these are all working fine for me now! 
I hope this helps someone else out there who faced the same issues as I have. 
For further reading please see the link below:
(Steam/Troubleshooting - ArchWiki)