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Don't buy any cards that don't work with Mojave, like HD 5780/6870/6890 or NVIDIA cards earlier than Kepler. Apple killed support for these obsolete cards.

Buy one of these if you need boot screens:
  • SAPPHIRE Radeon HD 7950 Mac Edition
  • NVIDIA Quadro K5000 for Mac
  • NVIDIA GeForce GTX 680 Mac Edition
You can buy the PC versions and flash, or pay someone to do the flashing part, or buy already flashed on eBay/MacVidCards. Read the threads about these cards and buy the one that fits your workflow best.
Hello! I have a question I'd like to ask you. My computer model is a Mac Pro (Mid 2012), with system firmware version MP51.0089.B00. Through OpenCore Legacy Patcher 1.4.3, I upgraded the system to macOS Monterey 12.7.3. Today, I replaced the original ATI Radeon HD 5770 with a PC version of the NVIDIA Quadro K5000 (non-Mac version). After booting up and hearing a thudding sound, the computer screen did not display anything, and the boot screen or boot selector did not appear either. Could this be because the PC version of the NVIDIA Quadro K5000 is incompatible with Mac? Is there any way to solve this issue? Thank you!
 
Hello! I have a question I'd like to ask you. My computer model is a Mac Pro (Mid 2012), with system firmware version MP51.0089.B00. Through OpenCore Legacy Patcher 1.4.3, I upgraded the system to macOS Monterey 12.7.3. Today, I replaced the original ATI Radeon HD 5770 with a PC version of the NVIDIA Quadro K5000 (non-Mac version). After booting up and hearing a thudding sound, the computer screen did not display anything, and the boot screen or boot selector did not appear either. Could this be because the PC version of the NVIDIA Quadro K5000 is incompatible with Mac? Is there any way to solve this issue? Thank you!

First thing, you need to upgrade to 144.0.0.0.0 to run anything later than High Sierra.


Second thing, PC GPUs do not have pre-boot configuration support with a Mac Pro, the display only works after macOS loads the GPU drivers. For pre-boot configuration support you need to make the GPU compatible with your Mac Pro, via flashing/EnableGop/etc.

With the two above, the easiest way to solve both is with a BootROM reconstruction service, two ducks in one row. I'll send a PM with all the info/service cost/turnaround time.

Third thing, you can't replace a GPU with OCLP, you need to unpatch the root patches and then re-apply OCLP root patches again. GPUs are not interchangeable with OCLP as with a supported macOS release. The root patches need to be re-done each time you change your GPU.

Make your GPU to work with High Sierra first
, be sure that it works correctly and only later you go with unsupported macOS releases.
 
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