Anytime I’ve used flex for a deposit the deposit and the actual closing transaction have shown up separately, with the deposit being returned shortly after the final payment.
At the beginning of my cruise I presented my flex card to be attached to my account, shortly after I received an activie card check, then a tiny <£0.50 hold. Today when requesting to settle the bill, they said they’d charge it to the card on file (I only ever tapped the card with contactless, so thought it would be unlikely to go through for an amount greater than the contactless limit) and sure enough Monzo prevented it.
After selecting in the app that I recognised the transaction, I asked them to try again and was told it went through. Looking at the app it seems they modified the original hold (<50p) to the full amount, rather than create a new transaction, though the foreign currency amount shown is still the original interestingly.
The hold transaction however was made during the previous payment window which finished 2 days ago. The increased amount seems to have been retrospectively added to this window, due for payment in 12 days.
Having previously used more ‘traditional’ credit cards, I found it interesting that they updated a transaction on what other banks would consider a closed statement which would have been finalised for a direct debit to be collected.