My guess is, that Meta will try to control the public image of the name Mastodon. Yeah the Software itself is OpenSource and protected under AGPL-3, but they still can buy Mastodon GmbH and use that to tie their name to Mastodon for the broad public.

They still have to comply within the 90 day period. If they can’t comply in that timeframe a warning or a fine could be issued.

You can find lemmy communities via the search function. Search with @COMMUNITY@LEMMY-INSTANCE, this produces a magazine that is linked to the community.