Question: In the UK, thanks open banking, couldn't you use a compatible bank like monzo and load all the other bank accounts via open banking into that single app?

Yes. Banks like Monzo allow you to import your other bank accounts into their app. I did it for a while, but ultimately I found it easier to just have separate apps for each. Most apps are very good and improving all the time, so usually one isn’t much better than the other.

I haven’t looked for a one-app-to-rule-them-all, but in principle it’s possible.

I think the UK banking sector is in rude health. It’s very competitive and it’s easy to move. The quality of the apps is very much part of any competitive advantage.

I have accounts with four uk banks and it’s trivial to manage them. It’s an example of legislation working really well.