Read the very last comment from a post started 2 years ago: https://forum.proxmox.com/threads/help-with-amdgpu-passthrough-for-lxc.136972/
#AMD iGPU passthrough LXC
2 messages · Page 1 of 1 (latest)
And here appears to be an even cleaner way to do it, with newer proxmox: https://github.com/tteck/Proxmox/discussions/2850