Below is my latest email... this one from GM corporate.
Thank you for prompt response and providing the requested information.
Based on our resources, there is a turn wheel on the left side of the steering wheel that you can roll up or down. This is the only way to dim the screen of your 2017 GMC Denali. This can be done while on the back up camera.
You may also check page 184 on your owner's manual under Instrument Panel Illumination Control. For more information about your Infotainment System you may check your ownerís manual on page 188 or you may call the Infotainment Customer Support Group at 8554283669. They can assist you with setup, navigation systems, download applications and system updates.
2017 2500HD Denali L5P