Secret shortcut to turn off screen that I can't find anymore

My computer is Dell Latitude 5400 and some months ago I searched in Google for something like this: "my Dell doesn't have Fn shortcut to turn off screen" and Gemini impressivelly gave me some secrect shortcut that worked. It was something like "Shift + Win + B", or "Ctrl + Win + T" or "Shift + Win + Alt + L" , I just remember with certain that it had "Win", a final latter and some additional key like "Shift" "Ctrl" or "Alt".

I was searching for it again but I can't find it anymore.