This is correct, in-app cheque imaging came to UK customers 2 years ago - although it took years and years of requests for it to be implemented. And when it was, there was a limit of GBP500 per cheque. You can also ‘freepost’ the cheque - for any value - to Monzo for a manual cheque-cashing service.
While the Monzo UK and Monzo US apps don’t seem to be feature-linked (understandably for most features) - seeing what the Monzo Ireland app delivers initially will be interesting.