Brightness slider control in Windows 10

Something that came up at work. Someone said that their display was too bright and that there is a setting in Windows 10 to change screen brightness (apparently adjusting the monitor wasn't enough) involving a brightness slider. I looked online and there seemed to be a way in Settings, System, Display, but I couldn't get the brightness slider to appear. However on a relations laptop it does work, see screenshot below. Does anyone know why it would appear on one windows 10 pc and not on another, please?
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