I can’t post on a Mastodon instance with another instance account, only comment on people’s posts. This is the same way Flohmarkt does federation.
Can you create a hashtag for australia with your account on a US server? Can you create a hashtag for France while living in Poland? Can you create a post with a hashtag for Romania while living in Scotland?
I also can’t create an community on Lemmy with an account from another instance.
I can easily create a post for any location without requiring an account for that instance.