Solution: increase systemd DefaultLimitNOFILE as explained here
I think that upon installation steam should increase the FD limit.
Hello @DougTy, @Guy1524, increasing FD limits is a privileged operation requiring root permission and most likely will not change any time in the future. This is also documented at https://github.com/ValveSoftware/Proton/blob/proton_3.7/PREREQS.md#fd-limit-requirements.
Phantom Doctrine (UE4) crashes on startup with esync enabled. With it disabled using
PROTON_NO_ESYNCinuser_settings.py, the game starts up fine. (however there are still some issues)In terminal while crashing: