Hit check for updates button to allow Windows updates download and install from Microsoft server,.Click update & security the Windows update,.Press keyboard shortcut Windows + I to open the Settings app,.If the brightness adjustment issue occurs immediately after upgrading to Windows 10 20H2, we recommend to check for and install the latest Windows updates that probably help to fix this problem.
Pro Tip: If you found that adjusting the brightness in Windows 10 settings works fine, but the function keys (Fn) of brightness control on the laptop keyboard doesn’t work, most likely you need to install additional software from the laptop manufacturer.
