oh you mean the little spline piece?
it can be a real bitch. sometimes you can use like a spark plug socket over the crank arm and smack it actually IN a few times to loosen it up. sometimes grabbing the basket with pliers and working each side trying to tug it out you can get it off.
unlike basically every other bike ever, it's not on a taper, so you should just be able to slide it out. if it's stuck, smacking it IN might bust it loose. also if you can grab it an turn it while the crank is fixed (rope in the cylinder as piston stop or hold the ignition side) that can get it loose. if it's super stuck you might just have to split the cases, which honestly isn't that big a deal. it seems intimidating but can be easily done in an afternoon.
Side note: don't use a standard piston stop in a sachs. it can fucks shit up bc angle plug.