Many "gamer" keyboards offer configuration software which allow assigning custom actions to key combinations (e.g. Fn+1), like launching applications.
You may also use the popular program AutoHotkey, to create a hotkey-script in windows, which will listen and launch your applications.
You did although asked for a single key action. There are certainly multiple ways of accomplishing this with a diy PCB, but I know of the product stream-deck made by the company Elgato. Their documentation shows under "System Action - Open" how to assign an action to a key. It appears to also work with Windows and MacOS.
Personally I pin my most frequent used applications in Windows to the task bar and launch the specific application via hotkey alt+taskbar_position (e.g. alt+3 for VLC).