FYI - This has been reported as a bug several times on other aircraft. It’s consistently occurring on several G1000-equipped aircraft.
But if you’re on PC in legacy mode there’s a workaround: hover the mouse cursor over the button and double-click both right and left mouse buttons at the same time. It’s hit and miss, but I can get it to work on all the G1000 rotary/push buttons.
It’s definitely a bug that the mouse doesn’t change to a pointer that works on a single click.