Oh yeah I found something similar just now which might work? Using DXVK_CONFIG="dxgi.maxDeviceMemory = 6144:" %command% to try and limit the game to 6GB VRAM. It hasn't crashed since, but I'm unsure whether that's because of this. I could try the other parameter as well and see if that works, though reading the comments I'm unsure about that. Worth a try
EDIT: I also found a comment on the NVIDIA forums detailing this solution. Apparently you can configure this system-wide, which would limit the VRAM on all DXVK games