Stay away from Plex, if you like to go with Free and Open source.
I'll start with Jellyfin, and Arr family (sonarr,radarr,prowlarr or Jackett), Vaultwarden and immich
Edit: Learn to spin up docker instances first, as above services would be easier to manage in docker containers and for back ups I prefer Duplicati. And if you run it 24x7 add AdguardHome or PiHole to the mix
Edit1: if you are extremely new to docker instances and find it hard to learn, just spin up CasaOS and you'll be good to go as it makes spinning up docker containers so easy.
True for users who are already setup with Plex, for them there is no reason to switch as of now, but for a person starting from scratch and setting up things for the first time, it makes a lot of sense to get Jellyfin instead of going Plex. As Plex is moving away from their core of making user's media available for streaming, and rather focuses in pushing its own streaming content (I know we can toggle that behavior off but it is headache fot new comers, and it should be off by default and if a person likes they can turn on Plex's streaming content, default should be the user's content)