Clean and rebuild your project. Unless you’re importing precompiled Swift frameworks, in which case they need to be recompiled too, long bless they’ve been built in library evolution mode.
Sounds like the SwiftUI frameworks are not module stable. Since they are still private frameworks, and are meant to work with a specific version of Xcode and swiftc, this makes a lot of sense.
Is the error message in your png resulting from building your "Hello, world!" app only? No other swift frameworks or modules are being used other than system frameworks?
Probably can't use the toolchain compiler because the underlying frameworks and other parts of Xcode that the compiled code relies on to actually display the canvas are probably not module stable, for the reasons I mentioned previously.
All of this is purely speculation until Apple chooses to comment on this.
I wonder what would happen if the OP actually built and ran the application using the 5.2 toolchain?
You’re probably right on that count. Personally, I haven’t yet been able to get a successful build out of 5.2 due to issues building some Combine APIs.
It’s not private, it ships with the OS like everything else, and it is built for evolution. However, it seems 5.2 cant see all of the symbols it produces, so I get errors on some APIs.