Why doesn't the brightness control work when running on battery power?

Question

laptops

Hey!
Help me please.
Dell laptop brightness does not change when running on battery power. All drivers and software are installed, Dell SupportAssist shows no problems. When working from the network, the brightness is adjustable, in the BIOS, the brightness is adjustable.
The matrix and the matrix cable were replaced.
What to do, where to dig?
A search on the forums did not lead to anything, except for replacing drivers, bios: I changed everything, but nothing helped, at the moment there are actual firewood and bios.

Answer 1

If you boot from LiveUSB of some Linux distribution, then there is also a problem with brightness (it changes from the network, it does not change from the battery), or does it only appear under Windows?
If only under Windows, then I vanguy that there is some kind of regular software from the manufacturer, which arbitrarily changes the brightness bypassing the power plan.
Also try booting in safe mode, some programs are not loaded in it by default.
And the version with clean Windows without official drivers, because. backlight auto control functionality can be in the drivers and override the power settings.