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.



https://github.com/marytts/marytts
I’ve used MaryTTS semi-recently. It’s older but works well enough for my cases. I have it running on a server (locally) and my endpoints make a call to it and playback the returned audio file.
On Android, I use SherpaTTS which has good voices, but I’m not aware of a desktop/Linux option. It mentions using voices from Coqui which you linked, so I would guess that would be the way to go for desktop.