iMac Upgraded GPU on High Sierra, then upgraded to BigSur Patcher, now won’t boot on High Sierra any more, only white screen.

[Paco Cook]

I hope I can get some help,

I upgraded My Imac 2011 27" GPU from the original 512mb to the a newer ADM Radeon HD 6970M 2048 MB, and it worked a charm on High Sierra

Then I upgraded to Big Sur Via "Big Sur Patcher", and all worked ok except the GPU acceleration, video is very slow.

So I decided to go back to High Sierra, but the computer won't boot High Sierra no more, it shows the apple, the booting screen and when it ends, it stays on white screen. So not even the recovery works or any system below and including High Sierra.

I will run MOJAVE, CATALINA and BSUR correctly in all, but the GPU acceleration. But not High Sierra any more.

I tried:

Reseting SMC, NVram, start on Safe mode, Recovery, Changed SSD with only HS, erasing / formmating the drive... >No Luck

I am not using OPENCORE (at least haven't even considered it)



I am inquiring from you If possible:

1) If its posible to accelerate my graphics card to run good on Bsur?

2) Go back to HIGH SIERRA (which worked fine before installing patched sur)



but haven't gotten any luck.



Please help



full specs:



iMac 27inch Mid 2011

3.4 GHz Intel Core i7 Cuad Core

32 Gb Ram

ADM Radeon HD 6970M 2048 MB

SSD 1tb System

HDD 1tb Data

HDD 1tb Data

 

[Nermal]

Does Cmd-V on boot work? If so, please post a picture.

 

[Paco Cook]

Does Cmd-V on boot work? If so, please post a picture.