So the solution detailed here worked, but what it says about Disney is unconscionable. Simply put, Disney developers made it impossible to use Hulu on an Apple TV 4K device without first installing their "My Disney Experience" App. I tried every possible permutation of password changes, one time passcodes, etc., with only the same results described here. Namely, I could gain access to Hulu on any device except my Apple TV 4K. Once I downloaded and went through the setup of the My Disney Experience app on my iPhone then, voila!, Hulu accepted the new password that I had created when creating a login to that app. What this says is that I had to give Disney more personal information in a new app that will be used to market to me in order to use the Hulu service. I have no plans to visit a Disney park, but if I ever do then the app is there. FRUSTRATING!