Check these possibilities:
● If an app or feature on your device is not working, not appearing, or is restricted (grayed out), a frequent reason is it may have been disabled using Screen Time, or by a technology 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 on an iPhone or iPad —> If your Apple Account is grayed out in Settings, or you can't sign out - Apple Support
Tap your Settings app > Screen Time > Content & Privacy Restrictions > scroll to Accounts > tap Allow Changes and turn on.
If the issue persists, also try going to Settings > Screen Time and turning off Share Across Devices
- If the device is managed (check: Settings > General > VPN (or Profiles & Device Management), contact the technology department of the organization that is doing the managing.
● If a payment method entry is greyed out and you are a Family Sharing member, you cannot add your own payment method unless you are the Organizer or you turn off Purchase Sharing. See How to share apps and purchases with Family Sharing - Apple Support
If you have a Family Sharing group with a minor child, that child’s account either has to be deleted entirely or it has to be transferred to another family group before either of you can leave the sharing group. See this article about how to move a child to another group using Family Sharing - How to transfer a child to another Family Sharing group - Apple Support