Those are actually not groups. Groups boost posts from all users that mention them. https://a.gup.pe/ is one implementation of groups with mastodon in mind, but lemmy communities actually work the same way when followed from mastodon. I believe other fediverse platforms implement groups in similar ways under the hood. This means that everything is more or less interoperable between platforms.

Tusky is a great app. But it doesn’t seem to have a trending tab, which I use to find cool accounts to follow. For now I use trunks.

Another good thing is putting people you follow into lists. I just wish we could do the same with hashtags.

This is how I mainly used Mastodon before Lemmy. It lets you follow topics instead of people; I prefer finding content this way. Unless a person really likes the format of Mastodon better, I’d suggest Lemmy over Mastodon for people that would rather follow topics than individuals.