The best way I have found is to wedge something under the drive coupler and then use a hammer or mallet to tap it off. It will allow the threading to grab and allow the unit coupler to come off.
Since you have to replace it anyways…I’d just clamp on vice-grips and bent it back and forth…it is a soft metal and will crack or such until you can get it off the motor shaft.
Since the drive is already stripped, probably the threads on the shaft are also fubared.