Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
You'll have to ask DosDude for permission, if he says its ok you can try it. JK! Your iMac should support 10.15.7 natively without a patcher. If you're looking to go unsupported, you can try OCLP and give Big Sur or Monterey a shot. I am running 12.1 perfectly on my Late 2013 but I just have Iris, no GT. Also need to boot from an SSD. Spinners are painful on anything newer than 10.13.
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.