I covered the optical flow sensor with piece of tape to remove this feature. The issue I am running into is I do not believe it is possible to control the speed of the drone without this feature.
What was the behavior of the drone during your test ?
The Anafi and Anafi Thermal autopilot can fly with a good speed estimation and control with either the vertical camera (optical flow) or with the gps. Furthermore during the same flight it is able to switch automatically between them depending on the quality of the measures of each one.
GPS estimation requires a good gps fix (orange or green gps icon on FreeFlight6) and the magnetometer to be calibrated. It is robust to short durations of magnetic interferences, like when passing near a metallic structure.
Optical flow is better when the ground is within measure range of the ultrasonic sensor (3 to 6 meters, depending on the ground type).
Some flight modes require absolute positionning, like RTH, FlightPlan, FollowMe, going to GPS coordinates. These are only available if the GPS is available.
When both the GPS and VerticalCamera are not usable by the autopilot (like indoor in the dark), the drone can still fly, there is no software code to forbid the takeoff. However it will not hover in place but drift at a speed around 1-2 m/s, and will drift with the wind if there is some. Manual control works, but is a bit more difficult, so it should not be done in small spaces.
have a nice day !