I know this is a bit stale, but I just fixed this problem on my machine. It was in the Intel Graphics Command Center => System => Power and then turn off "Display Power Settings"
Hello Dell and community,  I did a deep search of the web to find how to disable adaptive brightness but all the old solutions don't apply on the new XPS17. No BIOS option, no Power settings (adaptive brightness not listed anymore), no Intel settings, no active service that could be disabled - nothing. None of the old solutions work.  So how do I disable adaptive brightness control on the new XPS17 (9700, 4K, RTX)?  This is my main machine, I work on it ten hours a day, same as many people I suppose. So myself not being in control of the screen brightness, instead it automatically changing all the time based on screen content is not merely annoying. Any help would be very very much appreciated! thanks! Michael
XPS 17 9700 disable adaptive brightness control ???