The mouse wheel scrolls the graph vertically. If the Alt key is pressed, it will scroll the graph horizontally.
The Page Up and Page Down keys scroll the graph vertically. The keyboard arrows can scroll the graph if they reach the node border and cannot jump to another node in the specified direction.
Scrolling the graph does not change the keyboard cursor position. As soon as the graph is refreshed on the screen, IDA will scroll the graph so that the keyboard cursor becomes visible.