Apple removed Carbon and made Catalyst generally available in the same version. So they weren't ever viable at the same time. And can you point to even 1 developer considering a brand new app that doesn't support the last 2 OS versions?

Why stop at Carbon if you count removed frameworks? They had Classic and X11 too! And HyperCard!

Catalyst is expressly for porting iPad apps. So it's just SwiftUI and Cocoa if you compare macOS to Windows.