Silly question but what is your question? Yes you can run jellyfin in docker in a VM on Proxmox. Personally have a similar setup and I don’t use GPU encoding or decoding.

Also GPU passthough to a VM with vfio is generally pretty good and stable so if you want GPU acceleration it shouldn’t be to hard. I personally run a virtual machine for gaming that has a GPU and USB controller passed though to it. I can’t even tell the difference in terms of hardware performance