Important
Apple only returns the user object the first time the user authorizes the app. Persist this information from your app; subsequent authorization requests won’t contain the user object.
(https://developer.apple.com/documentation/sign_in_with_apple/sign_in_with_apple_js/configuring_your_webpage_for_sign_in_with_apple)

So you should go to Settings->ID Apple ->Password&Security and remove the app from apps that use your Apple ID

Now you can register again and apple will send the userInfo.

Important
Apple only returns the user object the first time the user authorizes the app. Persist this information from your app; subsequent authorization requests won’t contain the user object.
(https://developer.apple.com/documentation/sign_in_with_apple/sign_in_with_apple_js/configuring_your_webpage_for_sign_in_with_apple)

So you should go to Settings->ID Apple ->Password&Security and remove the app from apps that use your Apple ID

Now you can register again and apple will send the userInfo.