Can the internal flash of the camera (RX100 V) be used with the Sony MPK-URX100A UW housing? External diffuser? Preparations for screwing on external features?
The housing includes an accessory shoe to which an optional flash can be attached, a screw thread with three holes for an optional bracket and a handle, and a filter holder with a diameter of 67 mm to attach an optional filter or attachment lens.
External flashes should always be attached via an arm. Flash control via fibre optics is only possible to a limited extent with these transparent housings. In general, however, I would rather spend a little more money on a more professional housing: Fantasea, Sea2Sea, Ikelite or Nauticam. Nauticam is also aluminium, but not exactly cheap.