Apple iMac 27-inch, Mid 2010 Memory 4 GB. Not Used Since 2015 | eBay
Incase anyone ever needs the answer…I have a 27” 2010 iMac working in Target Display Mode with a M1 MacBook Pro using a miniDP to USB C adaptor that's capable of 4k60Hz.
Apple iMac 21.5-inch June 2010 3.33GHz Intel Core 2 Duo (BTO/CTO) – UNICOM, Inc.