With i install and play i get the same issue as you, vram filling up, framerate going down, ground texture going grey and if i alt-tab at that point the game crashes.

What i have done and works - at least in my case - is the following:

• dxvk.conf with memory limit in ../steamapps/common/Diablo IV/
• gamemoderun %command% in steam launch options
• textures set to medium in game.
• proton GE 9-15
• I also have the high resolution assets disabled in the dlc options in steam.

I can play fine with these, vram never goes above the limit i have set in dxvk.conf. I am doing this on endeavour, default kernel (not zen), 12500H and a 8GB 4060.

The limit i set is at 6GB for the vram. The only difference might be that this is a laptop with igpu so anything else OS related is rendered on the igpu and i don't use a second monitor. It plays fine and i can alt-tab without issues.

I am using a logitech g502 that has pretty much everything you listed as important. 0 issues with it on linux and you can even customise the onboard profiles with piper. Everything on it just works.