Were you using the flatpak of the server, or of Jellyfin Media Player, the client? Is the server on the laptop too, or just the client you were streaming to?

From what I understand (probably wrong) but you can get it to work, but it requires passing the device through. Sort of like in a docker container.

I discovered that intel has an equivalent for nvidia's nvidia-smi tool for looking at GPU usage, it's intel_gpu_top in the igt-gpu-tools package and Jellyfin is able to use my laptop's igpu. I might need to replace the thermal paste and clean out the heatsink.