use imac as a second display
I do have an iMac late 2014 - El Capitan os 10-11-6. I want to use it as a display and connect it to my mac book pro 2021. (I do have all the needed cables like thunderbolt, etc) in order to do that my imac version should be high Sierra or Sierra or earlier version. Apparently I cannot upgrade my imac version to any version after el capitan. Please advise how can i use it as the second display.
iMac 27″, OS X 10.11