What OS is needed to hook up an 2011 iMac to MBP

[brainwave89]

I have a 27" inch 2011 iMac that I need to use as a second screen on a 2017 MacBook Pro with 2 USB-C ports. What OS does the iMac need to have in order for this to happen?

Thank you for looking.

 

[padams35]

Supposedly any OS. https://support.apple.com/en-us/HT204592