> The FB case in US seems a bit stupid as what exactly do they have a monopoly on.

I have no idea what this measures, but Googling "Facebook markert share" shows lots of results over 50%: https://gs.statcounter.com/social-media-stats

> An upcomer like Tiktok can upstage them and create its own space out of nowhere in a couple of years.

Is it a requirement of a monopoly that no competitor could possibly come and grab part of the market? Like as soon as one manages to do that, there's no longer a monopoly, despite the relative market shares?

Also, I'm not sure I'd see them as direct competitors per se - in some spaces yes, but not in every space. TikTok is great for people who want to post videos, but not everyone is into posting videos. (Not sure why YouTube is listed on that page either, for the same reason.)