Maybe one of those HDMI “stick” PCs you can get? There’s x86 Android builds you can run or you can do like I did with my media PCs and boot into Openbox and just launch a fullscreen browser right to Jellyfin and control it from your phone. (My main setup uses Emby but should be able to do the same with JF).
I’ve actually got a portable Jellyfin server I take with me. Built on the OrangePi Zero 2W with a USB->NVMe acting as media storage (as well as the Jellyfin DB). It’s got several other services running as well as a second Wifi adapter so it can also act as a travel router.
For playback, I pretty much just use my laptop or phone but have thought about adding one of the “stick” PCs as a client for it.









Yeah, I don’t know about pre-installed with Android that aren’t ad platforms masquerading as consumer hardware. I’d never use one unless it was supported by LineageOS or something. My comment was more “roll your own” in nature.