A potential federation with Threads (should Thread decide to implement it) would overwhelm Lemmy/Mbin/Piefed with millions of users (compared to the 40k monthly current active users), transforming those platforms into a threaded version of Facebook
The easy solution is to just go to an instance and browse their All feed and see if it has the content you like. If I understand correctly you are limited to instance communities if you aren't signed in so that should give you a good idea about the instance culture.
For example, if you visit https://startrek.website/ you will see it is pretty much star trek stuff. If you go to hexbear you will just see their hexbear bullshit. Both will give you an idea of what their instance is all about without needing to register.
The easy solution is to just go to an instance and browse their All feed and see if it has the content you like. If I understand correctly you are limited to instance communities if you aren't signed in so that should give you a good idea about the instance culture.
For example, if you visit https://startrek.website/ you will see it is pretty much star trek stuff. If you go to hexbear you will just see their hexbear bullshit. Both will give you an idea of what their instance is all about without needing to register.