First of all, ensure that you did not enter information from a Form 1098 (mortgage interest statement).

Next, read all the way through the thread at the link below (you might be encountering something similar in this year's product).

https://ttlc.intuit.com/community/taxes/discussion/why-can-t-i-enter-my-property-tax-info-for-2019/0...

Thanks for your rapid response! I read through the link and it describes the steps I took three times this afternoon.  I saved the return I was preparing, exited from the program, relaunched the program and stepped through the prompts until the "Enter property taxes you paid in 2020" screen appeared. Two of the three entry boxes (Main House, Additional Houses) did not allow data to be entered; the third entry box (Foreign Real Estate) was active and allowed data to be entered.

@kforseth 

Did you read the last post in that thread? Were you able to resolve the issue?

I did read it and it did not resolve the issue. Perhaps the issue will clear itself up when the next TT update is sent out.