mastodon.social is one of the many independent Mastodon servers you can use to participate in the fediverse.
The original server operated by the Mastodon gGmbH non-profit

Administered by:

Server stats:

336K
active users

Are they adding ads to the main service, or are they creating another payment option with ads? That is to ask if they are going the youtube route (but reverse) or something dumber.