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.
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.
Plex app is better, but still inadequate compared to Infuse.
What about moonfin? I use it on shield and it works great.
Infuse is terrific software, and supports jellyfin and smb. I use it for jellyfin and absolutely love my setup.
I ditched plex because of missing Dolby audio support and all the use hostile channels and “features” years ago, and will never look back.