I did exactly the same for a while. Then I realised the planning features in Monzo, specifically Summary, were useless because it was getting limited data. At that point, I shifted everything across to Monzo, salaries, all bills, all outgoings, everything.
I still use YNAB because the one feature that Monzo currently lacks - forecasting - isn’t yet here. I know, I know, YNAB also isn’t a forecaster but with the YNAB Toolkit running, the overall balance in the future works really well to show me if I’m going to hit a negative figure at some point in the future unless I act now.