It's transcoding because Jellyfin decided it needs to transcode for some reason, frustratingly. I've converted to formats/codecs I know the TV supports, and yet Jellyfin still transcodes, with a message about the TV not supporting the codec (yet if I play the file on the TV from a thumb drive, it works fine with the crappy built-in media player). I'm using the Jellyfin client on the TV because it's easy to install without a Samsung account, and I don't think I can get Kodi on it (besides my experience with Kodi is not great, it's sluggish on real hardware, I can only imagine how bad it would be on an underpowered garbage TV and I don't know if a client exists).
From a bigger picture perspective, I think Jellyfin as a client will be better for my family. It's a simpler interface with less to get them in trouble.
I'll need transcoding for other/non-local devices anyway, so I still have to address the issue (annoying iPad for example).
If you have any advice about troubleshooting why it's transcoding, I'm all ears. This is the first I've gotten Jellyfin to work after multiple attempts over the years, across multiple servers and clients, so my experience with it is limited. I'm just glad it works at all - it's the first I've gotten to work other than Plex.
Thanks - at least now I know it shouldn't be transcoding.
I think the arrow is pointing at something that around here is called a potato.