Not sure if Starlink or Jellyfin issue..

[TheDreadPirate]

The ffmpeg log is still incomplete.

But in the main log all the transcode reasons are "TranscodeReason=ContainerBitrateExceedsLimit". Somewhere you have it configured that remote connections are transcoded when above a certain bit rate. This can be both on the client and on the server.

Change the bit rate limits so that it doesn't transcode.

And do you know if transcoding has ever worked? Is that the problem? Normally you don't transcode, but it is now and you are finding out it is broken?