encountered same issue, anyone solved it?

Wondering the same

This issue is bugging me from time to time. Had to delete the app more than 10 times. Anyone knows how to fix it permanently?

I experienced exactly the same. Interestingly, in about a month ago, everything sync as expected, it's not until recent few weeks that SwiftUI + CoreData + CloudKit no longer sync even after a long period of time. I tested both my old projects and Xcode's SwiftUI template(after adding necessary steps like enable CloudKit, etc). I can confirm your findings, that it no longer seems to sync in a reasonable amount of time.

.windowStyle(HiddenTitleBarWindowStyle()) will not work because that API is not available for iOS app with a macOS running destination.

Same here. Running on a M1 powered Mac. Xcode will freeze when I change tabs or doing something that is supposed to be lightweight. The beach ball appears, and then beach ball freezes as well. Xcode Version 12.3 (12C33)

As I typed the bundle identifier for the demo app. It creates 10+ garbage containers along the way automatically. Guess those will be sticking with me for the rest of my life. I wish I could share an image. Just found out that the forum doesn't support image either. OMG.