If the motor is prevented from rotating, the current will increase (which is also the reason why the motor is easy to burn after being stuck). It is precisely because of the rotation of the coil that the current in the opposite direction to the original current is generated, which is the "back electromotive force".
The thermal power of the motor can only be calculated by the formula P=I*I*R, but not by P=UI, precisely because of the "back electromotive force".