iMax 21.5inch late 2009 - Screen Mirror/External Display

Hi there,

I have an iMac 21.5 inch, late 2009 (Processor: 3.06 GHz Intel Core 2 Duo; Software: OS X 10.9.5). I would like to use it as a second monitor for my MacBook Air (M1, 2020). I've purchased a USB-C to Mini Display Port cable in attempts to connect the two. The Command-F2 option doesn't seem to do anything to help the iMac register the MacBook, and the iMac doesn't seem to register the cord or MacBook at all when plugged in.

Any idea on how I can get this to work?

Thanks,