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-history.com / iMac (Mid 2010)
OWC in-Line Digital Thermal Sensor HDD Upgrade Cable for iMac 2009-2010, (OWCDIDIMACHDD09)
iMac 27-inch (Mid-2010) Core i3 3.2GHz - HDD 1 TB - 4GB | Back Market
Identify your iMac model - Apple Support
Amazon.com: OWC 2.0TB HDD Upgrade Kit Compatible With 2009-2010 iMacs, Includes: Thermal Sensor, Tools, 2.0TB Hard Drive : Electronics
iMac (mid 2010) Core i3 review | Engadget
Apple iMac 3.2Ghz i3-550 27-Inch (Mid-2010) *NO HDD/RAM* – MSU Surplus Store
iMac 21.5" 3.2GHz Core i3 /8GB / NO Hard Drive / 2010 - MacEnthusiasts
Apple iMac 21.5-inch June 2010 3.33GHz Intel Core 2 Duo (BTO/CTO) – UNICOM, Inc.
Apple iMac 27-inch (Core i5) Review | Digital Trends
iMac Intel 21.5" EMC 2389 Logic Board Replacement - iFixit Repair Guide
2010 Apple iMac 21.5" Core i3,16 GB, 512 GB SSD - used - iRedo
iMac "Core i3" 3.2 21.5" (Mid-2010) Specs (Mid-2010, MC509LL/A, iMac11,2, A1311, 2389): EveryMac.com
Apple iMac 27-inch, Mid 2010 Memory 4 GB. Not Used Since 2015 | eBay
Identify your iMac model - Apple Support
21″ Apple iMac Desktop (2010) – SmartGiraffe Computer Services
Apple - iMac - (27 inch, Mid 2010) - i5, 8GB, 256GB-SSD, High Sierra – Ordinateur St Joseph
