What I think is fascinating is not just that we applaud Monzo for this, but that we allow other important services that control our lives to get away with revealing nothing about what happened or what they've changed to prevent it. Can you imagine any large bank (for the US, say JP Morgan Chase, Citi, Bank of America, etc.) putting out a note with this level of transparency, accountability, and clear direction to change?
For more about what makes a good apology, see https://withoutbullshit.com/?s=apology&submit=Search by Josh Bernoff, a former Forrester editor and a very direct writer.