Desktop LCD monitor which allows backlight to be controlled in software
The standard is DDC/CI and seems to be widely supported - it may need to be enabled from the monitors OSD (mine was disabled).
softMCCS from ddc-ci.com allows lots of control but it's too low level technical for regular use.
Just to control brightness and contrast I'm using http://clickmonitorddc.bplaced.net (Windows).
Try either TwinkleTray (it works for me on Win10 2020) or Monitorian.
ClickMonitorDDC seems to be down/no longer supported.