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
iMac Intel 27" EMC 2374, AMD Radeon HD 4850 Video Card Removal & Repair - iFixit Repair Guide
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 :
How to Upgrade/Replace GPU Graphics Card on Mid-2011 21.5" iMac - YouTube
For iMac 21.5" A1311 Mid/Late 2011 6770 AMD upgrade Nvidia K610m 1GB Video Card | eBay
Cracking Open the 27" Apple iMac (2011) | TechRepublic