I figured it out just as your response was coming in! And yes, it is about some strange details with how TT handles dependent status, which seem incorrect – but anyway.
TT asks 2 questions about dependent status. First: "Someone else can claim me as a dependent on their tax return."
Second: "And this person will claim me on their 2020 tax return."
If you answer Yes to the first and No to the second, TT does not show you the stimulus question. I think that it should, since the official eligibility criteria is just about whether or not you will be claimed as a dependent, not whether or not you can be.
When I switch my answers to No for the first, the second question disappears. And the stimulus question shows up! This was the problem.
