How to get the iMac to work as a monitor
I want to use my iMac as a monitor for my MacBook Air. I have a thunderbolt cable I got from Apple today. My iMac has macOS Sierra version 10.12.6 and my MacBook Air has macOS Big Sur 11.4. When I press command F2 the iMac just has a grey screen. I have tried the trouble shooting tips by Apple to no avail.