I didn't see your post until now. I am running Ubuntu 23.04 with a 3080ti and the lastest Nvidia Drivers 535. I am using Proton Experimental. I am also using DLSS with quality on a 4k TV. I get around 100 to 120 fps. I tried Vulkan and DX11 and they seemed to perform the same, so I stuck with Vulkan.
I know my graphics card has 12gigs of memory. Not sure about your model.
Did you ever get your issue fixed?