https://developer.apple.com/documentation/pdfkit/pdfdisplaymode/twoup

Apple's PDFKit allows to show two pages of a PDF side by side. PSPDFKIT (which is what Good Notes 5 uses) should support the same option.

I'm currently using the iPad 12.9 and typically have it in the horizontal orientation and there's soooo much wasted screen real estate. When making notes on a book or a large report, it's helpful to have more context on what is before and after the content. PDF books are often typeset such that content being read on a left hand side has images or quotes from the right hand side, and context is currently lost in a single page.

GoodNotes 5 has replaced my notetaking + planning + ebook reader applications. This is the one feature will push it over the top in my humble opinion.

Although GoodNotes 5 currently supports the iOS built in split view, it's not as nice when trying to view pairs of pages from the same book in split view. Moving forward requires two swipes on both the left window and the right window. Additionally, it limits use of other applications for split view.

Ideally, I'd like to be reading a book or report in split view, and making notes along that way. Occasionally, I'll need to check YouTube or Wikipedia or a Thesaurus for additional information, which can allow the GoodNotes 5 split to change back to single page. Once I'm done with the split, I can close it to return back to a twoUp view.