icloud backup from iPhone not working after upgrade to ios16.3

Hi really confused,

If you're looking to turn on Advanced Data Protection for iCloud, this does require two-factor authentication. This is explained in more detail here: How to turn on Advanced Data Protection for iCloud

Two-factor authentication isn't required to back up to iCloud. When two-factor authentication is on, you can set up other trusted devices and phone numbers which is recommended in case you do not have access to your devices. This is explained in more detail here:

With two-factor authentication, a trusted device or trusted phone number helps verify your identity when you sign in to a new device or browser.

What is a trusted phone number?

To use two-factor authentication, you need at least one trusted phone number on file where you can receive verification codes. If you have a phone number that isn't associated with your trusted device, consider verifying it as an additional trusted phone number. If your iPhone is your only trusted device and it's missing or damaged, you won't be able to receive verification codes required to access your account.

This information is from Two-factor authentication for Apple ID.

Let's continue with working on getting your iPhone backed up to iCloud. If you've already completed the steps provided previously, try powering off your iPhone for a few minutes. Restarting will help refresh the iPhone settings and can help with backing up. Follow this:

1. Press and hold either volume button and the side button until the power-off slider appears.

2. Drag the slider, then wait 30 seconds for your device to turn off. If your device is frozen or unresponsive, force restart your device.

3. To turn your device back on, press and hold the side button (on the right side of your iPhone) until you see the Apple logo.

Restart your iPhone

Take care.

Hello really confused,

If the iCloud Backup toggle is greyed out, the steps below may help:

1. Check if a restore is still in progress. Go to Settings > [your name] > iCloud > iCloud Backup. If your device is still being restored, you see “This [device] is currently being restored and will automatically back up when it is done.” You can create a new backup after your device finishes restoring.

2. Check whether you installed a profile that restricts iCloud Backup. Go to Settings > General > VPN & Device Management to see a list of installed profiles. 

You can also find those steps in this resource: If you can't back up to iCloud - Apple Support

Should that still persist, are you still able to sync items like your photos and contacts with iCloud?

Also, are you experiencing the same behavior with any other devices?

Let us know, and we'll keep moving forward based on those details.

Thanks for keeping the thread informed really confused,

We can verify the feature works on iOS 16.3, so we're confident the issue occurring on your iPhone can be resolved.

If you haven't yet, next force the Settings app to close, so a fresh instance of the app is launched the next time you tap the icon, than try enabling your iCloud backup again.

The following page explains how to force an app to close: Close an app on your iPhone or iPod touch - Apple Support

If the issue persist, providing additional information about any other steps you've already taken, can help members of the community provide relevant steps that haven't yet been taken.

Cheers!