alt Hacker NewsStarling also has a disaster recovery system across cloud providers, although it is implemented differently to Monzo's (I used to work there on multi-cloud).
Multi-cloud is really tough, tbh. It's easier said than done, especially if you care about data consistency at all.
I have built these system for financial institutions since before cloud providers. It is hard/impossible if not well constrained at a level that supports data availability and consistency well (ie using a proper database with the correct setup across all locations with the underlying OS configuration/patches applied uniformly - the latter lesson cost IBM a lot of money due to system downtime for a financial institution that I brought back online). Many software vendors offering on-prem versions don’t know how this works well exactly, so I’ve had to help them along the journey and get them to sign-off for their contractual obligations to be upheld in the setup.