When following an instance, the delivered posts are public posts on the other instance -- aka the "site stream". No private posts or private media are included.

You can follow it by putting the baseurl of the site into the 'new connection' box. To unfollow, delete the connection. This does not remove any other you connections you have on that instance.

This has been available for quite some time, but has only been lightly tested, hence my message. I'm just trying to increase exposure. If you encounter any issues or have suggestions, you know what to do. The original intent was for sites to connect with each other into federated community groups and make content discovery easier for smaller sites by following larger (trusted) ones without needing to enable the horrid 'public stream'. It wasn't until later I thought about letting normal channels follow instances, and sure, why not... Anyway that's the concept. I fully expect that it will evolve in ways I never anticipated.

This will probably only work with instances of the streams repository because it represents a third party relay. Might work with Mastodon which supports LD signatures but a lot of projects will just toss the relayed posts.

It's also theoretically possible to turn the site actor into a group. Then it should behave slightly different from what I described and appear to others as a bona-fide group. I don't remember if this part works or not. I haven't looked at it much in the last 2-3 years because I've been busy with other stuff.