Most Internet users who have used Facebook and likes? (And even I, who never have used Facebook, primarily use that sense.) It is the first sense in the Cambridge dictionary [1], the second sense in the Oxford dictionary available via Google Search, and the second sense and also the first non-academic sense in Wiktionary [2]. It is clearly common enough for me to say so.
Yes, but even if you take the first definition of the Oxford or the second of Wiktionary, then still would Mastodon be a Social Network, as it does match both descriptions.
Common to whom?