"Remote follow" is very unintuitive, particularly for Twitter users.

1. View a user's profile page on another instance.

2. Click "Follow".

3. A "remote follow" window opens with the message "Enter your username@domain you want to act from".

4. ???

How profile pages are displayed changes depending on whether you middle/right click ("open in new tab") or left click on a user's name from your own instance. If you left click, you get the profile page on you own instance. If you get the link by any other means (including e.g. someone sends you a link to their profile), you get the above. It's confused me more than once.