TL:DR; use catalyst (AppKit support has many performance and stability issues). UIKit is getting better over time so hobby projects are probably okay, but production SwiftUI apps are a risk at best. Improvements are part of the OS, so your users will need to stay up-to-date.
"If you are curious about SwiftUI, please don’t let this stop your enthusiasm. It’s clearly the future at Apple and all these issues will be resolved within a few years."
Seems like a long time to wait
I waited switching from objC to swift until we got swift4.0 with a stable abi. I’ll do the same for swiftui and wait till it becomes matured enough. As you said, it is good for hobby projects but not good enough for business.