Matrix is the closest thing. It doesn’t use activity pub but it is federated. https://matrix.org/

Have you heard of https://cosmic.voyage/ ? It is a community scifi universe of sorts

There is karrot (https://karrot.world/) not federated, but still interesting

IMO Solus Budgie is the most user friendly distro that I know of for non-techie people with Linux mint being a close second. I think others have already mentioned Solus in the comments, just thought I’d add a second vote :) My mom is using a Solus machine and my high school sister is using Linux mint. Neither is a techie.