That is what happens though, no money is taken from you until it settles, it’s just that Monzo show you your amount with “pending” transactions included. Please note that behind the scenes monzo works exactly the same as any other bank. If you put a lot of pending transactions into any other card it will also eventually fail due to insufficient funds, you just wouldn’t know what pending transactions caused this. Monzo gives you that complete visibility.
When pending transactions are not collected, other banks update your available balance behind the scenes, Monzo ““refund”” you this amount. Again no money actually moves, what Monzo do is update your available balance as you see it, again giving you a better understanding of what your available live funds are and what transactions have affected this.
Willing to bet a few pennies that these have run two authorisations on the card with the intent to only collect the later. Hotels authorise a deposit which they never take if all goes to plan and on checkout they charge your bill to the exact amount. The first authorisation allows them to collect money if they find out they need to fine you to cover costs, but more often than not they expire.
Again, with any other card, the double amount would be unavailable to you. With Monzo, it will feel like it is being refunded once it expires.