I’ve found Android TV to be the most usable TV OS tbh. I use Konstakang’s LineageOS Android TV 15 image on a Pi 5 which is source available (non commercial only licence). And Projectivy Launcher (closed source but is by an indie dev and better than the stock Google one). The Pi is CEC compatible so I can control it with my TV remote no problem, and I use Moonlight to stream games from my PC.

If you already have hardware, there may be an Android x86 TV release somewhere but I haven’t personally tested any, and you have to make sure the apps you want support x86 (all the open source ones like Jellyfin should)

Edit to add: I also personally haven’t found a need to install GApps as all the apps I use are either open source, or were made to work also on FireTV so don’t rely on GApps APIs. (Use SmartTube instead of YouTube, it’s a better experience anyway)

I built a near identical server for my parents and just sync my nextcloud folder to theirs using syncthing