For iMac 27" A1312 Mid 2009 2010 2011 upgrade NVIDIA K4100M 4GB GPU Video Card | eBay
Flashing a GTX 765M for Mac using nvflash - YouTube
GPU replacement program announced for 2011 iMacs, Apple to offer refunds for previous service | Engadget
Big Sur on iMac 27", Mid 2011, flashed 4GB NVIDIA Quadro K4100M by Nikey22, having issues with screen brightness, any ideas? Brightness control was working with Catalina Patcher, after installing Big Sur
Amazon.com: Valley Of The Sun 2GB Graphics Video Card Upgrade for Apple iMac Mid-2011 27 Inch Core i5 MC814LL/A MC814 A1312 Desktop All-in-One PC, AMD Mobility Radeon HD 6970M Replacement Repair Parts :
SOLVED: What GPU's are compatible with iMac 27" 2011? - iMac Intel 27" EMC 2429 - iFixit
Apple Initiates Video Card Replacement Program for Radeon HD 6970M Equipped Mid-2011 27” iMacs