iMac mid 2011 27 inch K2100M video card GPU upgrade 2Gb

In the end, I went ahead and installed this graphics card. Right after installation, the iMac rebooted, and as you could see in the video, it worked. The only disappointment was that the F1 and F2 keys, which control brightness, didn’t work.
Anyway, the card was already flashed for my iMac, which is exactly what I was looking for. At first, I tried the MonitorControl app to adjust brightness, but unfortunately, all the sliders were greyed out and didn’t work. Then I installed BrightControl, but it turned out to be a pseudo-solution: it really does dim the screen, but the iMac starts overheating quickly, because the panel itself still runs at maximum brightness and the program just overlays a grey filter. That was definitely not acceptable for me.
After a long search, I finally found a real solution. I downloaded OpenCore Legacy Patcher. It took me quite a while to figure it out, but here’s the process:
Download and install OpenCore Legacy Patcher on your Mac.
Prepare a USB flash drive (at least 4 GB).
Run the program and build the image directly on the USB drive.
The program will reboot your Mac automatically — hold down the Alt (Option) key.
Select the EFI menu entry, then boot into your main macOS.
At this point, brightness control should already be working. If everything went smoothly, repeat the process — but this time install the build directly onto your main HD disk EFI partition. Don’t worry, it’s safe to do so.
After that, you just need to press Alt again, boot with the new EFI, and brightness control will work natively. Once done, you won’t need to repeat the process again, even after shutdowns or restarts.
Thanks for watching! I’ve also added some additional files with research on which graphics cards work best for your iMac — you can download them under the video.