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.
Target Disk Mode - Wikipedia
Target Display Mode with an iMac - Promise Pegasus R6 & Mac Thunderbolt Review
Use iMac as monitor: 5 Solutions - 9to5Mac
Diagnostic boot of one iMac into another using target disk mode. - YouTube
Using Your iMac as a 2nd Display - Cable Matters Knowledge Base
Target Display Mode And Thunderbolt
Using an iMac as a Monitor in Target Display Mode
Luna Display's Target Display Mode Feature Adds Ethernet, Thunderbolt - The Mac Observer
Target Disk Mode - Promise Pegasus R6 & Mac Thunderbolt Review
How to Use Your iMac in Target Display Mode - YouTube