Not experiencing any mouse lag/issues personally, but screen tearing (specifically, every time I move the mouse it jerks randomly to a different location in my field of vision) makes the game unplayable until about five to ten minutes into each session, whereupon it randomly just stops? Haven't found a fix yet but idling the game on starting is a temporary solution.

Using "WINEDLLOVERRIDES="xaudio2_7=n,b" PROTON_NO_ESYNC=1 %command%" in the launch options as well, which fixes the muted audio and a little bit of the screen lag I noticed before setting the custom launch option.