Hi Michael. I also use (and rely on) YNAB for managing finances and use it with Monzo, albeit less-and-less as Monzo add great features. I’m UK based by the way.
I’ve got my Monzo Joint Account and my Monzo Personal account to automatically add transactions to the corresponding accounts in YNAB. It’s a bit technical to set up and relies on an external service to run, but it has been solid for me since I started using it 18 months ago. The Topic & instructions are here;
Good luck 