Adobe's documentation states:
Press the Left and Right Arrow keys to change the number of columns. Press the Up and Down Arrow keys to change the number of rows.
Hold down Ctrl (Windows) or Command (Mac OS) and press arrow keys to change the spacing between the frames.
I have NO problem generating additional rectangles instances up and down, left and and right, using the arrow keys but, for the love of me, I can't change the "spacing" : how on earth is a user to do that with the Control key?
Ah! Just "succeeded" now but it's not exactly ergonomic: I had to bring the mouse as close as possible to the right side of my keyboard so that I could, using my small finger, keep the left button of the mouse down while, at the same time, using my left hand, press the Control key down AND with my right hand thumb, press the arrow keys up, down, left and right.
This is plain silly? I must be missing something really obvious.
Know that I'mn on an extended keyboard layout on Windows 11.
There are two Control keys on this keyboard, one to the left and one to the right BUT the one on the right does not do anything with InDesign....
The spacing between columns is by default the same as defined for gutter in the document setup dialog. That mioght help you.
I'm on Win10 and have no problem with the Ctrl key on the right.
When I press the Ctrl key on the right, in conjunction with one of the arrow keys, I get the same effect as though I'd have only pressed the arrow keys alone, adding or removing additional rectangles 😞
But your put me on the track to a potential culprit: my keyboard layout.
I use the Canadian Multilingual keyboard layout by defaut but I sometimes switch to the US English keyboard layout: I just tried changing the spacing using the right Ctrl key using the US English keyboard layout and it works!!