Wiggle the wing test. One fellow rocking the wing tip.  Yaw damper linear actuator responds.  Rudder perfectly opposes each swing of the vertical fin

Copy this link for video:

https://youtube.com/shorts/HSCOv7yR17M?si=lkw_B7UvkRsMeXUN

 

Power up self test on F900, SPZ 8000.  Video shows reaction with hydraulic power applied.

 

If no hydraulic power is applied, you can feel it in the rudder pedals.  This one is particularly weak.  The servo is possibly failed.