Sorry for the delay in getting back to you.

I hope I ran the vkgears test correctly?

Yeah, that's fine.

Both of those should be using hardware rendering, at least based on my understanding of the text. You have the name of your video card where "llvmpipe" would show up, right above "64bit", which is what happens on my system when using hardware rendering.

But...for some reason, you're consuming a ton of CPU time when rendering using OpenGL, despite doing hardware rendering. That's not what happens on my system. I don't know what would cause that.

One would want it fixed either way. For Steam, one can force Proton to use OpenGL rather than Vulkan as a Direct3D backend by setting the environment variable PROTON_USE_WINED3D=1, which will cause many Windows apps to use OpenGL...but your problem is the opposite. Vulkan looks fine.

thinks

The only thing that comes to mind would be that there's an Nvidia mechanism on systems where you have multiple GPUs

this can happen when you have an integrated on-CPU GPU and a discrete GPU on a laptop, say -- to render on one and then copy to the other. I don't know what text would show up as the renderer in that case, and I don't have Nvidia hardware, much less Nvidia hardware plus an integrated GPU to test. I don't think that that's probably what's going on here, but I don't know what mangohud reports in that case. I would think that mangohud would be smart enough to actually display the renderer being used, but...maybe it's not. But if you want to try it, you could give this a shot. I'm taking a stab in the dark rather than really analyzing it:

$ __NV_PRIME_RENDER_OFFLOAD=1 __GLX_VENDOR_LIBRARY_NAME=nvidia MANGOHUD_CONFIG=full mangohud glxgears.x86_64-linux-gnu

If the CPU usage when you run the above command goes from ~20% (as is currently the case for glxgears in your above screenshot) to ~4% (as is currently the case for vkgears), that might be what's going on. If it is, then I'd try running your game with the __NV_PRIME_RENDER_OFFLOAD=1 __GLX_VENDOR_LIBRARY_NAME=nvidia environment variables set. I wouldn't bet much money on it working, but I guess it's not hard to try.

EDIT: If anyone else with an NVidia card wants to run the MANGOHUD_CONFIG=full mangohud glxgears.x86_64-linux-gnu command and report whether their system uses a ton of CPU time on all cores, that'd be a useful data point; I can't, as I don't have the hardware. I guess it's possible that that the CPU usage could be normal

this is going through xwayland, and maybe something there causes that. I don't want to flag it as something abnormal on OP's system if it's not. But it's not the way my AMD system acts.