In trying to assign functions to a profile in 11.5, where can I find the "Autopilot Master" selection? It doesn't seem to be under the Autopilot category. Thanks!

You need to look at the bindings under the "autopilot" subsection. X-Plane distinguishes between FD (flight director) and AP (Servos) and there are several options in that subsection, so you can choose which ones you want to disconnect. There are other options to engage the autopilot systems (FD and Servos) as well.

Which bindings would you suggest I use for Autopilot Master On and Off? Thanks again!

I am using the command

Disco servos, flt dir.

(sim/autopilot/servos_fdir_off)

to disconnect the autopilot and resume manual flight without flightdirectors.

But a more realistic option would be to bind two keys (buttons), one to

Servos toggle.

and one to

Flight directors toggle.

 

"Servos Toggle".