Upon looking to this further I’m not sure if it actually works as I understood it to, due to the way group services are handled currently in Mastodon. Clearly there is some sort of flag in Activitypub on group accounts to indicate to other apps that it is a group account, because e.g. https://lemmy.ml/c/[email protected] works and you can follow it but the same link substituting /c/ for /u/ does not work. And for normal user accounts, the inverse is true.

However, aside from that flag, my understanding is they are essentially just user accounts that boost any posts from followers that mention the account handle, which causes the boosted post to show in the feed for all followers of the account. Since that account isn’t actually posting the posts that it boosts, I guess it makes sense that activity wouldn’t be visible in Lemmy, where boosts don’t exist. Following this logic no posts would be displayed, and that’s what is observed. Initially I thought this was because no one on the instance had followed the group yet, because e.g. https://lemmy.world/c/[email protected] does show posts while https://lemmy.ml/c/[email protected] does not. The same group on a.gup.pe also shows more posts on https://lemmy.ml/c/[email protected].

It’s hard for me to make sense of what’s going on here (especially as I don’t microblog or use Mastodon personally) because clearly the Mastodon content is federating through the lemmy instance, but I’ve only been able to observe a subset of it and I haven’t been able to figure out the parameters that have caused some posts to be visible in Lemmy but not others.

I think “communities” term is used on Mastodon in reference to what are “instances” on Lemmy. I’m talking about communities as they apply to Lemmy - in Mastodon I think they’re generally called a “group” account. You subscribe to them in Lemmy mostly the same as how you’d subscribe to a Lemmy community on a different instance. e.g. go to your.lemmy.instance/c/[email protected] and subscribe. Or just search for the Mastodon group on the Lemmy communities page, making sure the filters are set to “All”. To find a Mastodon user page is the same, just /u/ instead of /c/. You just can’t follow or subscribe to the user pages because that’s not currently a feature in Lemmy, but you can for groups/communities

Watch history is an absolutely essential metric for Youtube - I can understand how you’ve been led to believe that turning this option off is opting out from that data collection, but no. What this setting is asking is if you want the data collected to be represented to you as recommendations for other videos to watch. It absolutely doesn’t change what data is collected, just whether the videos you’ve watched should be accounted for when the algorithm is finding new videos to recommend.

My understanding is that isn’t correct - in Lemmy you currently can follow Mastodon communities, but not users (following users on any fediverse platform including Lemmy itself just isn’t a part of Lemmy yet). I believe it’s planned to be implemented, but this is one thing differentiating Lemmy and Kbin - you can currently follow Mastodon users in Kbin, and in that case I think it’s just the same way you’d follow another Kbin user. To find their user page it would just be kbin.social/u/[email protected] instead of kbin.social/u/user, so I assume it would be similar for Lemmy once implemented