I tried running The Piano using Proton and it launches to the main menu but I can't click on any option using the mouse or keyboard. I have to Alt-F4 to quit the game. The Steam AppID of the game is 788610. I added PROTON_LOG=1 %command%
to the game's launch and got the following log:

steam-788610.log

I have checked whether there are updates for my system available and I am up to date

System Information:

Distro: Manjaro

GPU: RX 5700 XT

Driver/LLVM version: Mesa 20.1.6/10.0.1

Kernel version: 5.8.3-2-MANJARO

Proton version: 5.0-9

https://gist.github.com/Simmonz/f0df669d3365f50c9db9668010e824f5