Mxsmanic wrote
At least on the 737-800, the yaw damper can be turned on or off at
pilot discretion.

Turned ON and OFF...Yes, but hardly at the pilot's discretion.

I have no 737 experience, but the 727 has 2 rudders and 2 yaw
dampers. If just one of them fails, the pilot must descend below
30,000' and slow to a specified maximum speed, just in case the
other one should fail also.

Bob Moore