I don't use Monzo, so there's still the question of what does the UI show when they can't confirm the name - how much do they emphasize that everything now hangs on the account number only?

The bank app I use always shows a confirmed name if there is one. The UI problem is that when there isn't a confirmed name, they just do nothing, and say nothing.

Also, for very large transfers, the UI should do more than just tell you that the name can't be confirmed. The app should also encourage you to pester the receiving account holder to sign up for confirmation, especially if they are in the business of receiving large bank transfers (eg real estate & lawyer holding accounts).