yeah as far as I know, that’s the only way to subscribe to communities that aren’t on your instance. If you visit a community that’s not on the instance that you made your account on, it will say this in the corner (for example): “You are not logged in. However you can subscribe from another Fediverse account, for example Lemmy or Mastodon. To do this, paste the following into the search field of your instance: [email protected]”