I have actually managed to get NVIDIA and amdgpu working together. You can't use the NVIDIA as scanout card, but you can use it to render and then shift the output to the scanout on the amd card. You do also need to seperate out the userspace running the application being rendered by the nvidia system from the userspace of the host scanout in amdgpu
You're likely to get artifacting and stuff will break because nvidias glx is not compliant with the floss stack and that can cause issues. If you want to avoid those, then use a virtual output and sunshine/looking glass and access it that way which ensures you don't get the artifacts/issues with prime render sharing that the first approach introduces
Iuno I purged all but one NVIDIA card from my systems a few years ago. I keep a low power 4060 in a thunderbolt3 dock just for Green Team testing. After 20 years of fighting nvidias driver stack ( and still having some of the same bugs from 20 years ago). I have been much happier since moving to amd