Are only community names searched, or also posts, comments or usernames?

You can search whatever you want. The app doesn’t matter, what matters is the instance, which brings me to this:

Do the results of the search differ depending on which instance I am

Yes, basically (for posts), each instance cache subLems that at least one user from said instance subscribed too. Then, when you search it searches all the subs that it cached. So, if one instance unnfederate another instance, you won’t see their subLems at the search.

IDK how it works with subLems searching, I think you can find subLems that no one from your instance sub to, so my guess is that it asks each instance it federate with to get a subLems list and show all those to you.

You can search by:

• Subscribed = only communities you’ve subscribed to
• Local = only the instance you’re a part of
• All = all instances that have been federated with your instance, including your own.

You can also filter by specific communities, creators, or by keyword(s).

If you want to add a community from another instance that you can’t find in search, you can either enter:

• !communityName@instance.name Or
• Paste the full url into your instance’s search bar. It may take some time to find, subscribe, and sync to it though.

You can search for more communities at browse.feddit.de. Also, it’s easier to just do this from a browser rather than the apps available.

As for apps- Jerboa for Android and Mlem for iOS.