Game crashes on startup when using resolutions >1080p. I have a resolution of 2560x1600 and added a virtual desktop with the resolution of 4000x2500 to even start it up. Afterwards just toggle with a shortcut which can be set in the keyboard shortcut settings of your linx distro to fullscreen. Et voila: Fullscreen with 2560x1600 without any issues.

Protontricks is really key here by adding the emulated virtual desktop with a way higher resolution. Now it works perfectly and even sharper than windows.