Using mid-2011 iMac with new MacBook Air as dual monitor

I’m attempting to use my old 2011 iMac as a dual/external monitor with my new MacBook Air. Through my research I think I’ve determined that I’ll need a Thunderbolt 2 cable to plug into the iMac and then a Thunderbolt 2 to 3 adapter to connect to my MacBook. Will this work? Some places that I have read have made it seem like even this setup would not get me my desired display.