As far as I can find, Plex does not support AMD iGPU for transcoding. Jellyfin will work, but support seems rather spotty. For other AI/ML work, it seems like ROCm is up and coming, but support - e.g. for Frigate object detection - is still a work in progress, especially for newer chips.
I have an AM4 AMD iGPU I use with Jellyfin; it works fine.
Jellyfin supports it, but the resulting quality is noticeably poor compared to Intel QuickSync or software transcoding. Perhaps the newer chips are better, but if you're building a media server from scratch you'd probably build around an Intel CPU or ARC GPU anyway.