Before this fix, SFM was pretty much unusable, as menu contents were not visible and the program would crash while loading a map with this following Engine Error:

"failed to lock vertex buffer in CMeshDX8::LockVertexBuffer"

However when launched with "PROTON_USE_WINED3D11=1 %command%", SFM works without any issues or crashes and so far has been a very smooth experience to my astonishment. I even have been able to successfully export clips at 1920x1080/60FPS (slowly albeit but only because my computer is a bit of a potato). Audio also works if anyone was curious. Menu contents are now visible unlike before. I'm still rather new to SFM so perhaps there are some issues that I've not noticed yet, but again, everything so far seems to be working just fine and the program is doing its job. Will no longer require a Windows install to work with SFM.