Welcome to TVPaint Community forums !

Can you please explain a bit about the functionality of the new shortcut? I have 8-10 image marks in my timeline, but when I hold down the shortcut (Image Marks: Flip), it appears to flip back and forth between the two closest to the playhead. I would like to see it flip through them all. Is this functionality controlled by the light-table mode?

no, it was just for the next and previous Image Mark.
We can imagine better later, but it was the need of the moment for some of our users.

OK, thanks for explaining. Great feature to have!