What does it mean when it says I have to “verify my identity with Apple support”?

“verify my identity with Apple support”?

When are you seeing this request?

You will be prompted to do this, if your AppleID has been disabled for security reasons, or when you forgot your password and cannot prove your identity with one of the options that are available. Then you need the help of AppleSupport to establish your identity by contacting Apple Support with a phone call.

See: If your Apple ID is locked or disabled - Apple Support

Frequently asked questions about iCloud Keychain - Apple Support

Everything you need to know about iCloud Keychain - iMore

macOS Sierra: Set up iCloud Keychain - Apple Support

An essential Mac OS X Keychain guide - Computerworld