I have assigned a button on my joystick to ‘Autopilot off’, ‘Set autopilot disengage’ and ‘toggle disengage autopilot’ but none are able to activate the autopilot disengage button on the yoke. Having to grab your mouse, look down and find the button on the yoke is annoying especially on busy and fast approaches.

Yoke AP Disconnect
The Autopilot Disengage button on the yoke is actuated via the AUTOPILOT OFF keybind. You need to press it a second time to cancel any AP DISC warnings.
Please verify the button you are using is mapped only to that keybind.

AP 1 Master Switch on Glareshield
The TOGGLE AUTOPILOT keybind is used to toggle the AP 1 Master Switch between the CMD and OFF positions. Note turning AP 1 Master to OFF via this keybind will trigger AP DISC warnings that must be further cancelled via the AUTOPILOT OFF keybind which actuates the Yoke AP Disconnect.

See for reference this post: https://forum.inibuilds.com/topic/36540-tm-mode-goes-to-000-epr-if-ap-is-off/#findComment-89422