I am unable to turn off two-factor authentication

Once you have activated two-factor authentication and had it for two weeks or more, you cannot turn it off.

From this support document, Two-factor authentication for Apple ID - Apple Support

Can I turn off two-factor authentication after I’ve turned it on?

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, however, you can unenroll for a period of two weeks. 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 a higher level of security.

AngelaMarie818 wrote:

I am unable to turn off two-factor authentication anymore, how can I turn this off? The choice is not available in my apple id or iphone anymore.

When you first enable it you have 14 days to turn it off, after that you won't be able to.

AngelaMarie818 wrote:

I never turned it on, it automatically did it with an update. But now I cannot sign into my apple TV anymore.

It doesn't automatically turn on, you're ask if you want to turn it on and you can decline it.

If you have a newer version of iOS, that is why. See the information in the support document I linked.