1 - Boot Single User (press Command + S) at boot (If you have MacOS installed on your hard drive).
2 - If you have a blank HD, then use the USB stick/Pendrive with the MacOS installer (El Capitan, Sierra or HighSierra).
2.1 - Press Option key at boot, Position the mouse on the MacOS installer icon.
2.2 - Press Command + S and keep holding these two keys.
2.3 - Click the MacOS installer icon -> continue holding the Command + S keys until you finish the MacOS installer Single User boot .
Enter these commands (change gpu-power-prefs to Intel GPU and boot verbose):
Code:
nvram fa4ce28d-b62f-4c99-9cc3-6815686e30f9:gpu-power-prefs=%01%00%00%00 nvram boot-args="-v"
reboot
You can read the complete post here:
https://forums.macrumors.com/threads/force-2011-macbook-pro-8-2-with-failed-amd-gpu-to-always-use-intel-integrated-gpu-efi-variable-fix.2037591/
It's long and take time Good luck
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