Mlem developer here. We updated the app to version 2.0 about two weeks ago, which introduced quite a lot of changes. Mlem version 1 didn't offer a way to see the list of local communities, though - maybe I'm misunderstanding?
To see the list of communities for a given instance in the current version of Mlem (2.0), you can:
- Go to the search tab
- Open the search bar
- Type a space
- Tap on the filter button (just below the "cancel" button)
- Tap on "Any instance", and choose an instance to filter for
In the future we'd like to make the local community list accessible from the instance page, too, which would make it easier to find. Here's the GitHub issue for that feature.
I hope this helps.