My new iPhone 16 Pro Max will not backup to iCloud automatically

My new iPhone 16 Pro Max will not backup to iCloud automatically. It is connected to Power, locked, connected to Wifi and has more than enough iCloud storage space.

I already called Apple support yesterday, they said all my setting are ok and told me to reset Network setting which I did but it did NOT help. It will not backup to iCloud automatically even over Cellular. Manual backup works. My old iPhone and my wife's iPhone do backups every night with no problem. What should I do now ??? TIA