I hope you have a great time at Oshkosh. That is something I have always wanted to do, but have never done.
To answer your question. HDR is off in the System>Display settings. I dug a little deeper into System>Display>Graphics>Graphics Preference and Checked the [Don't use auto HDR] box.
Interestingly, Now the cockpit flood light does not illuminate the ambient space as before. It simply responds like the Taxi, Landing, Wing Ice Inspection & Cockpit Map lights by animating the light fixture to "on" but no 3D lighting occurs.
Also, When I loaded the aircraft, I noticed that the bezel soft keys on the G500 were illuminated, as was the Baro knob on the pilots standby altimeter and the center arrow of the autopilot panel "Turn knob". No power was on at the time.
Also, at launch, the aircraft seems to insist on selecting the windshield wipers to on.
Thanks Again.
Once again, Enjoy Oshkosh.... This will all still be waiting for you after the tents are all packed up and everyone has flown home. ;-)