brightness changes according to the content on screen.
it is "content ADAPTIVE brightness" or intel "digital power saving technology".
dell says it is a "feature" and WORKS "as intended"
it is very annoying while watching movies or doing any other simple tasks.
i tried some guides to tweak in registry but it doesn't worked
please help me to disable it.
That TOPIC was in the Dell support last month. Was that you?
https://www.dell.com/community/Inspiron/Inspiron-13-7373-Content-Adaptive-Brightness-Control/td-p/6090282
Inspiron 13 7373 Content Adaptive Brightness Control

And before that...
https://www.dell.com/community/Inspiron/Inspiron-auto-brightness-adjust/td-p/6066310
Inspiron auto brightness adjust

There are over a dozen post or links that sound just Ike your issue. I did not see any reference to a registry edit. At least one said you have to update the BIOS.

EDIT: This is not just about Dell. It is an Intel thing.
https://en.wikipedia.org/wiki/Intel_Display_Power_Saving_Technology

IMHO Thia was a dumb idea.It was never tested on a large group of people to see if it was acceptable to everybody. Of course, what I think does not matter any.

A Google search does not show any "fix" that will work for everybody. There is a post on Facebook, but it is not an official fix.

Do a Google for:
disable Intel Display Power Saving Technology
More... When you BUY a laptop, check for this:


Image of the control panel for Intel Graphics. Look for OPTION to turn off the 'feature'.