There is some grousing[1] that a cross platform technology, including Microsoft's own Xamarin, wasn't used and that fully platform native development is a waste. Was it mentioned somewhere specifically (maybe during GH the keynote that I didn't watch) that SwiftUI was used? That would be the only way to square the tweeter's statement that only 20% of mobile users would be able to use it, he must mean only those on iOS 13, but not totally sure. Hightlighting Dark Mode and a good iPad version would play into SwiftUI's narrative but the framework still seems a bit new for an app of this caliber.

[1] https://twitter.com/ThomasBurkhartB/status/11946837811956736...