I want to use my iMac (21.5", 2017) as a monitor screen for my Windows laptop (Lenovo). I went to the Apple Store today and there they sold me a HDMI to thunderbolt cable to do so. When I plug the HDMI cable in my laptop and the thunderbolt end in my iMac, nothing happens. I also tried turning both devices off and pressing command + F2 and command + Fn + F2 while restarting. Nothing happens.
Can anyone explain what to do?
Thanks very much,