Precision 5550 unable to adjust screen brightness - Despite all attempts

Pressing F6 an F7 brings up the slider but has no effect
Display settings menu slider also has no effect

Have run all F2 and F12 BIOS tests and no errors detected.

BIOS 1.38.0
Version ED 1.1.6

Display adaptors:

Intel UHD Graphics

NVDIA Quadro T2000 with Max-Q Design

Tried all the various solutions in this help community chat to no avail.

Thanks