How can I turn off two-factor authentication on a MacBook Air?

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Use two-factor authentication for security on your Mac, iOS devices, and iPadOS devices - Apple Support

If you already use two-factor authentication, you can no longer turn it off. Certain features in the latest versions of iOS, iPadOS, and macOS require this extra level of security.

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Two-factor authentication for Apple ID - Apple Support

See Two-factor authentication for Apple ID https://support.apple.com/en-us/HT204915 and more specifically the section entitled Can I turn off two-factor authentication after I’ve turned it on? You can't turn it off unless you recently updated your account. In this case, you can unenroll within two weeks of enrollment.

If you are in the two-week period, "Just open your enrollment confirmation email and click the link to return to your previous security settings. Keep in mind, this makes your account less secure."