Fixed by adding a dxvk.conf file on the game's root directory with the "d3d9.deferSurfaceCreation = True" option, although videos still don't work (thanks, ASF codec)
Tried proton 7.0, logs seem more in-depth, but problem persists (black screen on main menu, can navigate menus and all but, well, it's impossible to even try to load the game since you can't see anything). [steam-683280....