No, this is not a bug.
The question asks, "What type of High Deductible Health Plan did [name] have on December 1, 2020?"
It does this because TurboTax needs to know if you used the last-month rule for HSAs in 2020, and it couldn't very well ask you if you did, since most taxpayers have no idea what the last-month rule is.
The last-month rule states that even if you did not have full year HDHP coverage in a year, if you had HDHP coverage for the last month (which, in practice, means whatever you had on the first day of the month), you can take the full annual HSA contribution limit instead of pro-rating it.
If that doesn't make any sense, don't worry about it. Just break the question down into two parts: Did you have HDHP coverage (as opposed to regular health insurance), and was it on December 1, 2020? If the answer is "no", just answer NONE.