playback fatal error

[TheDreadPirate]

If you have AV1 content, and your device supports playing it, Jellyfin will just send it to the client unmodified.

The problem is you're try to transcode TO AV1.  Which your GPU does not support.

The list of boxes at the top are the codecs Jellyfin will send to the GPU for decoding when transcoding is required.  If they are unchecked, your CPU will decode those codecs.  If they are unchecked, that does NOT mean you cannot play them at all.

Use that Nvidia link I included in my prior post to figure out what your GPU can decode and encode.