I can only speak to Mullvad, but if you want to, you can visit their onion site on tor, and pay using Monero while providing zero information. They give you a 16 digit number. And that’s it. That’s the extent of your interaction with them. No name, no email address, no credit card information, nothing.
Most of that is optional, of course, but the option is always there.
I’m the farthest thing from an expert when it comes to programming, etc., but my understanding was that the FOSS end of it is more about which license you use to distribute, and whether or not you provide the code to the public?
I don’t really understand how that would affect the functioning of the app itself. But again, I’m not a programmer so maybe I’m missing something here.
I was having issues with it the other day, and so I pasted the URL into my browser and it would not let me watch past 1 min of any video without disabling ublock.
Needless to say, I didn’t watch the video. I’m done with using YouTube in any official way. If they successfully remove all options for avoiding ads on their site, then I will just never go there again.

Possibly related, but I was able to download a distrobox image of SteamOS through BoxBuddy. Dunno if it’s legit or what, but I was able to play games through it (though made no sense to). This was a week or two ago that I saw it on the dropdown when installing a new box.
Edit: I see other people in this thread mentioning some old steamos so maybe it’s that I dunno, maybe I will check later.
Yeah that’s my point