Thanks for the reply.
First, I have been using the Apple TV+ on my TCL television until recently when something changed. So, yes, the TV+ is definitely available in my region (USA). In fact, I’ve also been using the TV+ on my iPad (2nd gen) and iPhone 11. I have had no sign in issues on those devices.
Second my Apple ID should be set to USA. But I went to follow the instructions from your link. It did prompt me to sign in. Once I successfully signed in, it told me “You have one or more Apple TV subscriptions which must be cancelled before you can change your country or region.” Remember that I have been using the TV+ for over a year. It might also be worth noting that we do have a hardware Apple TV. It’s an older generation device. I’ve been able to use that too.
Third, on the TCL television, I had removed the Apple TV+ channel and reinstalled it. The sign in problem persisted.
Finally, I verified on my iPhone that my region is set to USA.
At this point, I will click the link above for support.