Why is my Apple ID disabled and how do I fix it ?

If your Apple ID is locked or disabled - https://support.apple.com/HT204106 - "If you or someone else enters your password, security questions, or other account information incorrectly too many times, your Apple ID automatically locks to protect your security and you can't sign in to any Apple services. You can unlock your Apple ID after you verify your identity."

What to do after [or before] you change your Apple ID email address or password - https://support.apple.com/HT204071 - Or if you're seeing persistent disabled messages.

If you cannot resolve it yourself:

Contact Apple for help with Apple ID account security - https://support.apple.com/HT204169