"Which" or "what" when there is a choice between implicit popular items?
Solution 1:
The answer at "Which" vs. "what" — what's the difference and when should you use one or the other? by sirmirzo says
We usually use which when we are asking about a fixed or limited number of things or people, and what when we are not. Often, however, we can use either which or what with little difference in meaning.
Note that (i) "usually" and "often" do not mean "always" and that (ii) the wording allows you some discretion.
There are no rules in English: there is guidance. Some guidance looks like a rule, it is not.