Can't sign out of Apple ID

This is caused by screen time restrictions. Go to settings>screen time>restrictions, and make sure that the switch to allow account changes is switched on. You can also try and turn off screen time altogether to see if you can sign out after that.

Hope this works for you!

If an app or feature on your device is not working, not appearing, or is restricted (grayed out), it may have been disabled using Screen Time, or by an IT administrator if you are using a device owned by an employer or educational institution.

- Read this support article If your Apple ID or other options are greyed out in Settings —> If your Apple ID is greyed out in Settings - Apple Support

Tap Settings > Screen Time > Content & Privacy > scroll to Allow Changes and turn on.

- If the device is managed (Settings > General > VPN & Device Management), contact the IT department that is doing the managing.