Custom Outlines have been added in the update 5.0.15. If you can't see the option to add pages to the outline, you are likely running an outdated version and need to install the latest update from the App Store. You can check your version number in GoodNotes > Menu > About.
Document outlines allow you to quickly navigate to specific pages in your documents from the Outlines tab in the thumbnail view, just like a PDF or ebook table of contents.
In GoodNotes 5, you can create custom outlines for any document in your library by adding pages to the outline.
How to add pages to the outline
There are two ways to add pages to the outline:
a) Tap on the ... button in the navigation bar of an open page and tap "Add this page to Outline"
b) Open the thumbnail view and tap on the arrow next to the page number and tap "Add Page to Outline"
You will then be asked to insert a title/name for the outline item, which will appear next to the page in the thumbnail view and in the outlines tab.
How to remove pages from the outline
To remove an outline item in the Outlines tab, swipe from right to left on the item.
How to rename outline items
The option to rename is not yet implemented but will be added in the future. For now, you can delete the outline item and create a new one with the desired name.
Tips & Tricks
Pages can be added to the Outline multiple times and thus can have more than one label. You can use this to tag pages in your documents.
Outline items are searchable from the search tab in the library & inside of the document.
Migrating old bookmarks from GoodNotes 4 to Outline Items
If you migrated your GoodNotes 4 documents to GoodNotes 5, your old bookmarks were converted to "Favorites". You can convert them to Outline items in Menu > Settings > Document Editing. Favorites you added in GoodNotes 5 won't be affected by this conversion.