Two part authentication
I am continually asked for two part authentication but my Apple iPhone 6s says that two part authentication is not available on this device
iPhone 6s, iOS 15
Question marked as
See the support article Availability of two-factor authentication for Apple ID - Apple Support
If you don't see a reason there then contact Apple about this:
Contact Apple for help with Apple ID account security' --> Contact Apple for help with Apple ID account security - Apple Support
"This article provides country-specific Apple Support contact information for customers seeking help with their Apple ID password or other security-related issues."