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Have you checked Settings/Screen Time for any restrictions?

Try a restart.

Restart your iPhone, iPad, or iPod touch         

Try a forced restart.

Reset Device.     

If necessary

Hard reset.        

If there are restrictions in Screen Time that are preventing access, you will need to restore the device to factory settings. Do not restore from a backup made when the Screen Time code was active.

If there aren't any Screen Time restrictions, do a backup and try a factory reset. Then restore from your backup.

Restore to Factory setting.      

Backup - Restore your device from an iCloud or iTunes backup.