How to turn off two factor authentication?

According to Apple:

If you already use two-factor authentication, you can no longer turn it off.

Certain features in the latest versions of iOS and macOS require this extra level of security, which is designed to protect your information.

If you recently updated your account, you can unenroll within two weeks of enrollment.

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 and means that you can't use features that require higher security.

Without going into too much detail or debating “why”; this in all likelihood is NOT going to happen.

So, you DO need to FULLY understand the “workings” of Apple’s 2FA.

Carefully reading - and re-reading - these two documents is the best place to start:

Two-factor authentication for Apple ID - Apple Support

Get a verification code and sign in with two-factor authentication - Apple Support

Suggest that you pay particular attention to the selection of your “Trusted Numbers” as they become essential to recovery if you loose access to your “Trusted Devices.”