On iPhone or iPad · Open the Settings app. · Tap your name, then tap iCloud. · Scroll down, tap Advanced Data Protection, then tap Turn on Advanced Data Protection ...
How to turn on Advanced Data Protection for iCloud
Extracted from the above link...
"Requirements...
To turn on Advanced Data Protection for iCloud, you need:
- An Apple ID with two-factor authentication.
- A passcode or password set for your device.
- At least one account recovery contact or recovery key. If you don't already have one, you'll be guided to set one up when you turn on Advanced Data Protection.
- Updated software on all of the devices where you're signed in with your Apple ID:
- iPhone with iOS 16.2
- iPad with iPadOS 16.2
- Mac with macOS 13.1
- Apple Watch with watchOS 9.2
- Apple TV with tvOS 16.2
- HomePod with software version 16.2
- Windows computer with iCloud for Windows 14.1
Managed Apple IDs and child accounts are not eligible for Advanced Data Protection."