Target Display mode is pretty Universal on the 27 inch iMacs from 2009 & 2010 with only a mini display port connection required. : r/mac
Instructions: Use the iMac as a Windows PC monitor »Sir Apfelot
iMac 27" (Late 2012) display connection to Macbook Pro 13" (2017) - YouTube
Can I connect my old iMac with a mini displayport in Target Display mode...
How To Use an iMac as a Monitor for a PC
How to Use Your Old iMac as a Monitor
Using an iMac as a Monitor in Target Display Mode
The Case of the Late-2012 iMacs - MacStories
Use iMac 27" in Target Display Mode with Raspberry Pi - Ask Different
Using an iMac as a Monitor in Target Display Mode
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.
How to Use Your iMac in Target Display Mode - YouTube