On Linux running on ARM CPUs it is currently not possible to run hardware transcoding even when the hardware is capable. For example, running on a Nvidia DGX Spark (which has NVENC support) does not allow hardware transcoding. I believe the Nvidia drivers are exactly the same API as x86_64 counterparts.
The only thing missing right now is the option to enable hardware transcoding. Seeing as future machines might include ARM processors more often while running modern AMD/Nvidia/Intel GPUs seems like this issue might happen more often in the future.
EDIT: Confirmed to work on Jellyfin, this is the support matrix for NVENC, all formats are supported on the DGX Spark:
