The correct way to disengage the Autopilot is to use the AP DISC button on the yoke. In MSFS the TOGGLE AUTOPILOT MASTER and AUTOPILOT MASTER OFF control assignments can be used to trigger the AP DISC button.

If the autopilot is abnormally disconnected, either by forcefully moving the yoke, by pressing the AP button on the center console, or due to a loss of power, then a continuous Autopilot disconnect warning will be audible. This warning can be cancelled by pressing the AP DISC button on the yoke.