Originally just on my gaming rig, but then I moved it over to the NAS. Synology has a community managed version, and there's of course docker.

Last month I finally got around to building a little server in an old office PC I grabbed on eBay. Moved all the apps from the NAS since the Celeron J in that isn't very powerful.

New server is an HP Elite desk 705 G4 SFF. Has an AMD Ryzen 5 Pro 2400G, 16GB RAM, 256GB NVMe, running Proxmox. Have Emby, Radar, Sonaar, Jellyseerr, Bazarr, Flaresolverr, Jackett, PiHole, and some other stuff all running there without any performance issues like before. An external Seedbox for downloads, and everything automated with SyncThing back to the NAS locally for the media apps to handle and send to Emby. Have an Intel Arc A310 SFF on the way to add to get AV1 encoding and future proof the hardware a bit more.

I've been slowly building up to this compexity over a decade or so now. In the beginning I just had a Plex server running on my desktop gaming rig and put media in the library manually. At some point I switched over to Emby instead of Plex, and I've automated most of it, works 99% of the time without me having to touch it now. Occasionally an automation step will fail (usually with rTorrent on the seedbox not moving completed downloads) and I'll have to do that step to get it back on track.

You can definitely go simple with just Plex/Emby/Jellyfin (all very similar media apps) running locally on your computer and put your media in the library folder manually and be done with it.