In the end, I worked around the problem by just starting a new return and doing it over. This time it accepted the responses, determined that I was eligible, and the screen that allowed me to enter the number of days worked from home appeared. I don't recall the exact sequence of steps that I took that got me into trouble the first time, but I understand that this is new functionality and likely still a bit buggy.
One thing I can guess might be the problem though is that on my first attempt I entered the T4 information, and then went back later to add the working from home expenses information. The second time I did it all in one flow, and that worked.
