I want a frame of an animation to show for some seconds.
I know that by CTRL-dragging to the right I can increase its duration- however:
If the (single) frame in question is followed by other frames (on the same layer, blank frames or not) then CTRL-dragging doesn't work.
What is the usual way of solving this problem- so that the frame becomes longer and subsequent frames are "pushed" to the right, not overwritten?
right click and click insert frame. you can also select a span of frame and copy and paste those to add many more frames if adding one at a time is too slow. and there are other ways to extend your timeline (like using f5 if you haven't customized that keyboard input).