Canceling HA or ACC is definitely a learned skill. But it makes sense. With 1-pedal driving, lifting your foot off the accelerator completely will cause the car to decelerate until it stops. With no foot on that pedal when you cancel, the car does what it would do if you lifted your foot off completely while driving at that speed.
So the trick is to start, despite intuition, by pressing down on the accelerator until you get to the point where you would need to be in order to achieve your current speed. Or at least have it down far enough that the initial regen will be minimal. Then press the X button on the steering wheel. Then slowly lift off the pedal again, as you normally would.
It’s not that hard, once you get used to it. Becomes second nature, like downshifting a manual transmission. But if you are used to disengaging cruise control via the brake pedal, it’ll be a bit of a learning curve.