Lemmy pretty much just needs tags. Like you can mark your different “technology” communities with the tag “technology” and a user can subscribe to this tag to view all posts from whatever communities have this tag (and they don’t have to call themselves strictly just “technology”)
Something like that I would imagine so no direct interaction between communities required.
To be expected. I like it but it’s still quite an immature platform overall. There’s lots to be done to make it easier for an average user.