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.