Cannot adjust screen brightness via DDM-2 when color depth is set to 10bps

When I set color depth to 10bps in color settings of Nvidia Control Panel, I cannot change brightness and contrast via Dell Display Manager 2 v2.3.2.18.  Settings are greyed out, although HDR setting is off. It seems a software bug on DDM2. Because I can change brightness and contrast via monitor's own menu.