This is where you put those flags?

I would also try without PROTON_USE_WINED3D=1.
Next thing I would try do redefine DEF_CMD in run script to point to FAF's exe
i.e. DEF_CMD=("/home/manjaro/kubo/.faforever/bin/ForgedAlliance.exe")

@nogthar it looks like PROTON_NO_ESYNC=1 PROTON_NO_FSYNC=1 is not applied somehow. Could you post your whole run file?

@fractal do I understand it right, that those who need to run it with D3D instead of vulkan needs proton 4.11?

yes (for missing vfx). I never used multi monitor setup, but I was able to use primary secondary output on 3 monitor setup with dgVoodoo (did not try without it :P). Be sure you have watermark in bottom right corner to confirm correct installation. And use 32 bit version of dll