read about the Boole object in the Help for more info but like a lot of C4D you add a Boole object (Create/Modelling/Boole or it’s in the interface under the Array object along the top of the viewport) and add the two cylinders as children of the Boole, then in it’s default mode “A Subtract B” it will subtract the second object from the first so if you get the larger diameter cylinder as the first child and the smaller diameter cylinder as the second object it should work like you want