Did you find a solution?
I think similar problems have been around for years and remain unresolved.
I’m having the same problem. I was able to correct the order in the theme files to at least be one under the other, but it doesn’t make much sense unless the main category and subcategory are visually separated. I made things better with ChatGPT, but this time I got errors on different backends. I will be very happy if dear Rahul can solve this problem, which will not be too difficult (for him).