Update 2: For additional context, my Apple ID is approximately 14 years old and is already a member of several Apple Developer Program organizations. I have normal access to App Store Connect and existing developer teams. The issue only affects enrollment into my own Individual Apple Developer Program membership.

Update: The behavior has changed now: On iOS, the Apple Developer app now shows a disabled “Enroll Now” button with the message “Enrollment through the Apple Developer app is not available for this Apple Account.” On the web, the enrollment page still displays “Your enrollment could not be completed.” In the macOS Apple Developer app, clicking “Enroll Now” results in an “Action not allowed” error.