The Apple TV solutions for Jellyfin are inadequate last I checked. Basically you are stuck with Plex and Infuse. I already have lifetime Plex Pass so no reason to care... for now.
Infuse is another $100 license to sync watch history, when I already paid $100 for Plex a while ago (with the primary driver being 'sync watch history', which is the basic feature Plex provides).
Paying more money to use a different product, and then expecting all of my users to do the same, is a big hill to climb.
For how much Infuse gets praised I was disappointed in the UI/UX. Playback is great, but the browsing UI is terrible and offline downloads are really buggy (Just like with Plex for a very long time)
It's worth noting that Swiftfin finally had a new release for tvOS this summer which is worth checking out if you're interested in Jellyfin on Apple TV
Not sure of your issues or when you last tried. I recently installed Plex on my TruNAS. I use the AppleTV app and it works well.
One caveat is that older AppleTVs can’t do native decoding of some mkvs. But that’s largely an AppleTV limitation. Though I could imagine the client being smart enough to list its abilities and the server only serving content supported by the client.
I ditched plex because of missing Dolby audio support and all the use hostile channels and “features” years ago, and will never look back.