Apple's mobile phone iCloud can't be synchronized because some projects are not turned on. You can go to the Apple phone settings interface and turn on some functions. Please refer to the following for specific operations.

Take IPhoneXS Max as an example:

1. Go to the home page and click Settings, as shown in the figure below.

2. Click the top account information in the setting interface, as shown in the figure below.

3. Enter the account information and click the icloud tab to enter, as shown below.

4. Enter the icloud interface, first turn off the backup switch of unnecessary photos, as shown below.

5. Then take the icloud interface to the bottom and find the iCloud cloud backup option to enter, as shown below.

6. Just turn on the iCloud cloud backup switch, as shown in the figure below.