An experienced user will know that this means “you accidentally opened a normal private window instead of a Tor window, and that’s why your URL isn’t working.”. A newbie, however, might think that
“This page has been blocked by Brave” means that a specific .onion site is forbidden in this browser in particular.
Suggested solution: When a user attempts to open a .onion URL in a normal browser window, the error message should say something along the lines of: “Open a Tor window if you wish to view a .onion URL.”