Would like the option to group a collection of pages within a notebook, and collapse / expand them to make larger notebooks easier to navigate.

Don’t want to create nested folders as this involves too much clicking around.

At the moment I create section heading pages and tag them as favourites, the use favourites view as a type of table of contents page like a book.

Would be better though if from the outline view you could group and collapse pages to make it easier to scroll through the groups, then select them to see the pages in sections to see the pages within.

Structure for outlines
Though adding pages to outline is a great feature, Goodnotes will be more convenient if we can have some simple structure for outlines such as a Chapter-section-subsection structure, which makes both pdf reading and handwritten notes much better organized within one notebook instead of creating multiple folders.

Totally agree
- those unnested sub-outlines appear along with the main outlines, making the outline page a big messy. To find a specfic outline, I need to sort through all the messy outlines

Yes!

Hope to make groups (sections or chapters) to organize my pages (that becomes too many..) in a systematic way.

The chapter can be separated as a new notebook if needed later.

Add Sidebar(support pin) to view outline with PDF files.

I do this using a separate sheet between sections but I'd really like a proper divider option.!

Creating dividers would allow sections in the notebook so there will be no need to create new notebook every time and will make things easy to find.

If I can categorically separate my notes within a notebook with the help of individual sections or chapters, and be able to quickly and easily navigate between these, it would be a handy functionality benefit.

This will allow the user to separate topics or ideas, while keeping the whole content in a single exportable notebook.

The pdf outline tab is a great feature and it is already incorporated.
It would be fabulous to use this collapsable outline to structure and easily navigate lengthier notebooks. For instance for study notes this would be more than helpful.
On the other i could often use these little red flags as bookmark signs like other apps have (bamboo paper, notability and most ebook readers). This is faster because you dont need to specify a bookmark text, you can unmark easily and you have a visual clue in the thumnail preview.
The bookmarks tab could then be used to show thumbnails of all pages with such a bookmark flag.

Some classes have very long slides making it hard to handle large amounts of bookmarks. The ability to nest bookmarks (like the PDF outlines) would be very handy.