You can just search for something like Android and it’ll show all the communities including the instance it’s on and join; you don’t need multiple logins.
The app I use, wefwef, also can view all communities in the feed along with your subscribed or just local instance communities. I’d assume liftoff is similar but I’ve never used it.
You only need to sign up for one instance. What app are you using or is it the browser?
A possible better solution might be to allow the user to create their own group (or super community if you prefer that name) where they can group multiple communities together in a way they see fit (not just necessarily clones of the same community. Examples could be a sports group that allows you to group together communities for all the teams you follow).
This would be beneficial I feel for most users, doesn’t affect decentralization, doesn’t require a central authority and would be only relevant to each individual user and not applied to anyone else
Exactly what gatob said. Lemmy is the platform that all instances (Lemmy.world, lemmy.ml, etc) connect to.
All apps work with all instances. There’s jerboa, connect, wefwef (soon renamed to voyager thank god), liftoff, with more coming soon (boost & sync of reddit fame)