Plex is a privacy nightmare that's slowly trying to faze out you having a server all together in favor of feeding you commercialized content from other providers; and many people find Jellyfin is far too unpolished/disorganized for a lot of debatable reasons I won't go into.
I've been quite happy with the middle ground: Emby. It's not FOSS, but is well polished with consistent development, great feature parity across platforms, excellent clients for pretty much every device I'd want to use, and a helpful community ready to assist with any problems you come across. They also have a heavy focus on privacy; with no third party partners collecting your info like Plex, and no telemetry sent from servers/clients.
The lifetime premier license I bought 7 years ago was well worth it.