You forgot an instruction "X - throw rock".
The brown bag says ""A brown bag with a feature of creating rocks from thin air when the button is pressed" but does not say which button to press to create more rocks. "X" is not the button; I have no rocks but I am in a puzzle where I must throw rocks at switches.
Thank you for reporting Mozai! I did put a tutorial on throwing AND refilling rocks, X to throw and hold SHIFT to refill rocks. But if you missed it you can go to the pause menu settings to see the controls (unless the SHIFT control is locked behind an unused ability which gonna be a bummer). I'll create more control view in the future.