I see, thanks. I did read that thread earlier. That's about banking/credit card. In any case, I'm only having this issue in the US.

That's one of the confounding things about my issue. They don't want me to use MFA to access my credit card or bank accounts. Or to book travel. It's ONLY the section where I want to convert miles to an airline. Perhaps if I set up MFA for my main credit card and banking access, it will somehow open up the mileage conversion buttion without then requiring MFA?
(Update: I tried to do that but there is no option for MFA on the website login!)