How to remove two factor authentication?

See: Two-factor authentication for Apple ID - Apple Support

You basically can’t anymore; it’s a fundamental element of Apple’s security architecture.

There is a window for 14 days after initially enabling 2FA for pre-existing accounts where it could be turned “off” — however you would have received a notification of this …

… so presumably you’d not be asking here if it were applicable.

Is there a particular problem you are having with 2FA? We can certainly assist.

Suggestion: DO read the article linked above carefully; paying particular attention to selection of your “Trusted Numbers” … these should generally NOT be numbers to your own Apple devices, but rather be alternate “disaster recovery” numbers where you can optionally select to receive codes via SMS or voice if/when you loose access to ALL of your trusted devices. (think fire, man-made or natural disaster)

Also, consider adding a recovery contact as an alternate recovery means:

Set up an account recovery contact - Apple Support

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.

Ok … lets troubleshoot assuming that we CAN’T turn it off.

The 2FA system should send the verification code to ALL devices already signed-in with the same AppleID via a “Special Pop-Up”

Is it doing this?

If you’re indeed getting SMS instead, it sounds like you might have the older 2-Step Verification (2SV) system … ???

If so, this article might be helpful:

(FYI, it sounds like 2FV CAN still be turned off under certain conditions)

Two-step verification for Apple ID – Apple Support (AU)

Yes, we’re all “good samaritans” here. 😇

Any “Apple Persons” present are clearly ID’d as being such.

And yes, this conversation has been “public” since your OP.

Neither we nor Apple can “turn it off” for you.

However, if you follow the linked instructions and determine that you indeed DO have the older 2SV (vice 2FA) …

… you should easily be able to turn it off yourself by following the same instructions (linked again below).

Two-step verification for Apple ID – Apple Support (AU)

Great. 👍

I suspect many will be interested in your findings.

Most haven’t encountered still-active 2SV in quite a while.