I mean, my Plex server is on a Fedora machine, it seems to be doing fine. I have gotten into arguments here about how frustrating it is that Linux advocates pretend every usability problem for Windows users is solved and that "just use Mint" is a valid solution to that issue. If you want to know how that goes, it goes a lot like this conversation.
On topic, using any external login or remote access third party service for your self hosted services is a significant change in how much info is not controlled by you, nobody is arguing that. There's a conversation to be had about whether that's worth it for most users. Like I said earlier, is it a good thing for Home Assistant to provide a paid subscription service that will handle that for you? For most people I'd say yes, it's still a much safer, more flexible alternative to Google's or Amazon's ecosystem, so why not? Baby steps.
But if you're already using a commercial service that already has a proprietary login then no, it doesn't matter. Plex already knows which clients go to your server. It does not need Google for anything here, having Google's SSO doesn't give them any information they already have. It does give that to Google, but if your concern is the cops are going to bang on your door for all your illegal pixels that you stream then you're just as boned. It's borderline irresponsible to pretend otherwise.
As for the "I have nothing to hide" thing... look, if you want to have this argument with someone else go pester them instead. It's not "I have nothing to hide", it's "this commercial service that I use does something that is legal and I intend to both take advantage of that and defend my right to own my media". How you get "I have nothing to hide" out of that is your own pretzel logic.
I have a right to store, backup and access my own media and to keep a copy of it for private use. I will exercise that right regardless of how many US corpos pretend that hey own the very concept of showing video to people. I am doing nothing illegal here and of the perfectly legal software options to do this perfectly legal thing I chose the one that had better usability for my family to be comfortable using it. This comes at the cost of an external service storing some of our data, just like our Netlfix and Disney+ subscriptions do, but since I'm not keeping a media server performatively that is a tradeoff we have made on a bunch of places because not everybody who lives here is willing to do homework to be able to use their devices. That cool with you?
For the record, I don't have any misgivings about FOSS as a concept. I do have remarkable contempt for people who want it to keep being a minority option because they like being in the secret treehouse and don't want everybody else learning about it. Widespread, successful FOSS doesn't look like half-baked UX and hobbyist programmers working for nothing in their spare time, and I would certainly like to see a landscape where alongisde hobby projects we have a solid stable of financially sustainable professionally made open source alternatives that anybody can get into. Jellyfin isn't even the worse offender here. If nothing else it's frustrating because it could be a more approachable sustainable alternative in the vein of your Blenders or Home Assistants... but it's kinda not, and that sucks.