I'm happy to watch ads so I don't have to pay for Instagram, Google Search & Docs, Gmail, Twitch, Youtube and most of my podcasts. I wouldn't be able to afford it if I couldn't pay with scrolling of my mouse past such ad (or my data, no worries)
I REALLY do not want to pay for a bunch of random services with my tax dollars. In your example, once I lose interest in youtube (or peertube in this case) I would still be paying for other people to use it and I get no benefit.
Right now, when I lose interest in Facebook (as I did) I just move on to the next service, it is unbelievably friction free. I just type a few letters in a URL.
Facebook dislodged Myspace, Tiktok is competing with Facebook, Discord is a brand new social media product. Anyone is totally free to create a subscription service or alternative (see DuckDuckGo). I don't understand the monopoly case.