Friendica is 16 years old. I started with Diaspora in 2011, but it never gained activitypub support. Friendica always had a multiprotocol approach and should still communicate with Diaspora.

There are organisations joining. EU as well as Germany on federal level and in some states have Mastodon instances. Dunno about the other EU countries. The German Heise Magazin runs their own Peertube instance in parallel to their Youtube account

I think it’s intentional that the fediverse doesn’t fully agree on how they do things. Lemmy and Mastodon can still communicate with each other way more than Reddit and Twitter. It was sad that PM was incompatible, but there is a lass severe cut if you switch services

Usenet still exists afaik