Some iCloud's data isn't syncing

Hi everyone. Recently I reset my iPhone 12 (iOS 17.5.1), there was a pop-up in Settings said that "Some iCloud's data isn't syncing" and it required my old passcode of the device. But somehow it kept denying the passcode (which I'm 100% sure about). Then I found an option to delete the end-to-end encrypted datas, but the problem was it just failed all the time I tried, said that I need to change my network and try again (I'd tried both Wifi and cellular network everywhere possible). Can you give me any solutions about my prolem, either way to delete iCloud's encrypted data or to get rid of the syncing pop-up. Thanks a lot!