adaptive brightness broken with Windows 11 Update (24H2)

[sda-ret]

I have a ZBook 15 G6 with 4K DreamColor screen that I have been delighted with ever since I got it.  Until this past week, when I updated Windows 11 to 24H2, at which point my adaptive brightness no longer works.  It is not a hardware issue, since when I enter a BIOS screen, the built in display is at full brightness.  But as soon as I enter Windows, the screen dims to about 30% of full brightness and there is nothing I can do to change it.  It shows at 100% brightness, but it is not, and moving the control from 0% to 100% is almost imperceptible. 

I've turned off adaptive brightness in Windows settings, re-installed video and hotkey drivers, updated the BIOS, updated a registry key per other posts here about brightness,  and even reseated the battery, with no difference.  I used System Restore to roll the machine back to pre-24H2, and that fixed it, but regrettably I forgot to tell it to not auto install updates, so it just reinstalled 24H2 and now I can't restore to a previous state.  Is this a known issue? 

Any advice?  At night, the screen is readable, but during the day when it is bright out, I can't even read the screen because it is too dim.

[sda-ret]

ok, it took some time, but I was able to recover this by downgrading the NVIDIA driver.   Usually, guidance is to upgrade to the LATEST/NEWEST driver, but in this case, it appears to be causing the issue.

The video driver from HP (sp153568) uses driver version 32.0.15.5612 dated 7/9/2024 (Jul 9).  It is apparently not compatible with the adaptive brightness feature as updated in Win 11 24H2.  I was able to DOWNGRADE the NVIDIA driver by going to the NVIDIA site and getting version 538.78 which is NOT their latest.  It has a timestamp of Jun 10, 2024.  But after downgrading, my brightness is restored to the way it was before I upgraded.  So I now have Win 11 24H2 and NVIDIA driver 538.78 and the brightness can be adjusted again.

I hope that by documenting this, I can save somebody else some time!!