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I consent to Plex to: (i) sell certain personal information (hashed emails, advertising identifiers) to third-parties for advertising and marketing purposes; and (ii) store and/or access certain personal information (advertising identifiers, IP address, content being watched) on my device(s) and share that information with Plex’s advertising partners. This data is used to deliver personalised ads and content, ad and content measurement, audience insights and product development. Your consent applies to all devices on which you have Plex installed. You can withdraw your consent at any time in Account Settings or using this page.
Soure: https://www.plex.tv/vendors/ (Might have to clear cache)
Can also read about the changes here: https://www.plex.tv/about/privacy-legal/
I haven't used Plex in a decade and I use Jellyfin, what you're describing sounds perfect. I read up a bit on STUN servers and it's what Syncthing uses, but they also mantain discovery and relay servers (and anyone can host one and can be added to the public list). Security wise they seem to be doing fine?(I'm not an expert, just an informed user)
Idk what combo Jellyfin would benefit the most from; are relay servers needed? The workload is similar but probably higher on average, people stream more often than they do backups