There are quiet a lot of feature request regarding being able to export all Highligthed parts of an PDF. However for a start i think it would be beneficial if, you could filter the (miniature) pages in the content view to show Pages that has been Highligthed or written a note on.
Kind off like the Bookedmarked tab shows only bookedmarked pages. For start it probably would be enough to show the entire page a Highligthed has been made. In a Perfect world (probably quiet challenging to archive) this could maybe work like the preview when searching for something in a PDF, so that only a small part (wich the marked) part is shown

I also would be a fan of a way to X-Ray or summarize marked bits like suggested here https://feedback.goodnotes.com/forums/191274-customer-suggestions-for-goodnotes/suggestions/19640692-a-search-engine-to-find-highlighted-text-on-ipad the idea is quiet old and got a lot of upvotes but hasn’t been addressed yet as far as I`m concerned.

Anyway i think my suggestion to show the entry page with highlight should be a good start.