I like reading comics and manga and marking them up. Goodnotes has the best markup I have tried. But there are some panels in the books that join into one, and when I import my PDFs I can only see half of the panel at once. I would like to be able to see two pages at once. Gapless would be ideal, but I imagine it makes sense for there to be a gap. A toggle would help.
Bonus Points if I can choose to read from right to left as well so I can read both comics and manga, and choose which document has which scrolling behavior.