Was able to start the game with and without the launcher. In launcher the settings option does not seem to work. Played the game on Win 7 some time ago, experience with same settings running it on Manjaro was pretty much the same. Very rare hiccups, freezing and crashes.

About Mods: There is a QoL Modpack wich doesent seem to work on Linux.

But there is a way to enable steam workshop and use Mods. Guide here: https://steamcommunity.com/sharedfiles/filedetails/?id=2410440667

I found the mentioned launcher.config file here: /home/USER/.local/share/Steam/steamapps/compatdata/235540/pfx/drive_c/users/steamuser/Application Data/Fatshark/Warhammer End Times Vermintide/