Not a whole lot based on our experience few months ago.
Coincidentally, 2 hours ago I submitted Molecule.dev right here to HN (an hour before this AWS submission), a full-stack solution which aims to address all of the time consuming pain points of building (common functionality), maintaining, and releasing cross-platform apps.
It isn't a UI builder like AWS Amplify Studio, but I think we can do it better. We cover all of the most common use cases and are planning on adding more, all without any vendor lock-in or unnecessary convoluted abstractions.
We'll also soon be rereleasing an email app using the Ionic option.