I would be happy to hear that the question works on your site. Unfortunately, that still doesn't seem to be the case.
I downloaded the question "quiz-ENA-Millman’s theorem-20201122-0922.xml" that you attached to your last post, and I imported it to my Moodle site. The question worked perfectly the first time without even editing it.
The question works when the question behaviour is set to either "Interactive with multiple tries" or "Adaptive mode". The disadvantage of the "Adaptive mode" mode is that the student must enter all the answers before pressing the "Check" button, otherwise the mark is zero. As I mentioned
earlier, it's probably possible to develop a workaround to solve this problem. But until then, it is easier to just use the "Interactive with multiple tries" mode.
I suggest you try the question again. Check the parameters of the question. Indeed, on your last screenshot, we see the green check mark (✔) which indicates that the answer is correct. However, the score displayed is "0",
possibly because of the penalty for each incorrect try and that you ran out of tries.
There is a small problem to correct when "reviewing" the question where a red cross is displayed even if the answer is correct. I know the fix, but hadn't applied it yet while waiting to see interest in this question.
On another subject, good news. As I told you earlier, not only do I think I know how to directly integrate answer boxes into a TeX equation, but I now think the method works. A few more tests and soon I should be able to implement this simple method in a few