The reason seems to be that I installed the app from testflight not from app store six days ago. In fact, the version is the same. But I don't know why iCloud doesn't sync with the app from testflight. I log in it with the same account.

I found that I have set the price of App. I have revised it to zero. It's free in App store now.

"Appeal to the App Review Board" works! My App is approved! I am so excited! If you are facing unfair review results, remember to appeal!

Hi, Zhiqiao, Thank you for your reply. It seems that the only way is to remind the users to sync iCloud across the devices by launching the app. Hope there will be smarter solutions from Apple in future. Best Wishes,

Hi, Ziqiao, Thank you for your reply. 1.We just enabled iCloud sync in our app by following the guidance(https://www.hackingwithswift.com/quick-start/swiftdata/how-to-sync-swiftdata-with-icloud). 2.The app is similar with apple calendar. The app sync events data across the devices. 3.We have talked with some potential users. Their habits are to edit their agenda on iPad or Macbook because the screen is big enough. And then they will carry their iPhone to go outside and depend on the notifications from their iPhone to remind them. We can remind them to launch the app on their iPhone to sync the data from iCloud but sometimes they will forget it. That's why we want to design some codes to sync the events data from iCloud in the midnight without launching the app on iPhone.We have designed codes to reschedule the notifications in the midnight via backgroundtask. It works well. But we can't find the method to manually sync iCloud data via backgroundtask. Look forward to good solutions from Apple for it. Best Wishes,