Filter Categories over Budget
Is there some type of "quick" filter to display only those categories over budget?
Nope. There's not even a reliable indicator there is overspending in the header. It's easy to miss if you collapse category groups. (Cash overspending is summarized in next month's header, which is awkward but better than nothing.)
I've suggested adding an overspending summary in the header that will move the focus to the next overspent category when pressed (scrolling and expanding the group as needed). You might make a similar feature request (form on the right side of the support page).
I don't think a filter to display overspent categories is the best thing from a holistic viewpoint, since the very next thing will be to move funds from a green category.