Viewing communities from other instances is a bit... unintuitive currently in Lemmy. For a remote community to be accessible, someone first needs to search for it.
Either as the full URL:
https://midwest.social/c/cats
or the search string:
[[email protected]](/c/[email protected])
I've just searched for that community by URL now, and it is showing for me on aussie.zone:
Another thing to note, is that posts/comments are only synced once someone has subscribed. So you won't see most older content. You can "pull" it to aussie zone by searching for full post/comment by URL.