I use OpenCore, on my 2010 27" iMac of all things. Needed to enable target display mode and native brightness control on the new K610m GPU. So in essence, my actual Macintosh is now a Hackintosh in Apple's eyes.
I did something similar.. I had an original Mac Pro, which didn't support 64-bit MacOS because Apple's UEFI ran in 32-bit mode and Apple's boot loader / kernel never supported switching into 64-bit mode from 32-bit mode. So to use that machine for 64-bit driver development, I had to make it into a "hackintosh", where they had a UEFI that would run in 64-bit mode..
If you have a 2010 or 2011 iMac with a dead GPU btw, check out this thread on the MacRumors forum: https://forums.macrumors.com/threads/2011-imac-graphics-card...