[m_mueller]

such as? If I remember correctly (has been a few years), over the last 15-20 years there were

iOS: UIKit -> SwiftUI

MacOS: AppKit -> Catalyst -> SwiftUI

there was definitely some churn within each one of those from version to version, but no complete rewrite needed afaik.

[pjmlp]

I advise then to pay attention to Apple developer podcasts for rants regarding each of them, and porting issues, you can start with ATP.

[m_mueller]

I listen to almost every ATP. I know the rants. None of them were along the lines of: Apple forces me to completely rewrite Overcast, or else it won't work on the next iPhone.

[tonyedgecombe]

I wouldn't even include Catalyst in the list. It is only relevant to a small subset of developers.