Older iPad

If you have enabled Apple’s new iCloud Advanced Data Protection feature on any of your devices that are running iOS/iPadOS 16.2 or later, you will not be able to sign-in with your Apple credentials on any devices that are not running iOS/iPadOS 15.x or later.

If you disable iCloud Advanced Protection on all your devices, you may be able to sign-in.

Should you wish to continue use of iCloud Advanced Data Protection, you will need to first disable Find My on the older device - then fully sign-out from iCloud - before enabling Advanced Data Protection for the newer devices. You can then continue use of the older device(s) using a different AppleID.

How to turn on Advanced Data Protection for iCloud - Apple Support

You screenshot clearly suggests that one or more your devices have not been updated to iOS/iPadOS15 or later - or macOS12 or later.

If all all of your devices are fully compliant with minimum requirements - and the error persists - you will need to seek assistance directly from Apple Support.

You can contact the Support Team using the Support link at top-right or bottom-left of this page. Alternatively, you can initiate and manage your support cases using the excellent Apple Support App. If not already installed on one of your devices, the App can be downloaded from the App Store:

https://apps.apple.com/gb/app/apple-support/id1130498044

Can you provide the precise wording of the error that you see - or post a screenshot (suitably redacted to remove of obscure personal data)?

For the benefit on absolute clarity…:

1) What model of iPad do you have?

2) What version of iOS is actually installed on the iPad?