If you start the game without changing any options in the menu, the cursor is hidden in the mouse view but the truck's functions menu is often non-responsive. Have to close the menu, click, and open it again.

If you do change some option in the menu, then the cursor is always visible, even in the mouse view. It usually appears as soon as I press the throttle pedal (using wheel & pedals).

I've found another way to unfreeze the functions menu is to press the throttle pedal (I use a wheel & pedals). There's some conflict between the mouse and pedals.