Do have a play around with the Table of Contents function @Luminary99_0 has mentioned above. I had also wanted folding headers, but I’ve found that the sidebar contents list is more useful since it allows you to see all the headers whilst still navigating. Plus the function works the same across different file types, e.g. PDF, so I just find it easier as navigation is the same regardless of what I’m up to.
We discussed it in another thread a year ago and I thought you’d like to see the other conversation about it, as I was in your position and introduced to the functionality:
(I still use {{TOC}} as well.)