Taken from StackExchange
Thanks to LangLangC
For temperature and other improvements see https://gist.github.com/cdleon/d16e7743e6f056fedbebc329333d79df
Shutdown, unplug everything except power and hold
leftShift + Ctrl + Option + Power I holded for 5 seconds, but holding just for an instant should work
Command + Option + p + rUntil you hear the startup chime two times.
if you are on high sierra 10.13.6+ you might need to use
Command + rinstead
Command + r + scsrutil disablenvram fa4ce28d-b62f-4c99-9cc3-6815686e30f9:gpu-power-prefs=%01%00%00%00nvram boot-args="-v"rebootCommand + sIt might look as if it hanged, but press enter and you should see the shell (root#)
/sbin/mount -uw /mkdir -p /System/Library/Extensions-offmv /System/Library/Extensions/AMDRadeonX3000.kext /System/Library/Extensions-off/touch /System/Library/Extensions/rebootIt will show a bunch of text in the screen (don't be alarmed, let it finish) and then it will restart again In second restart it will show text in the screen again and then it will show normal login screen Your computer now should work properly (dGPU off and iGPU on, shown as i in gfxCardStatus
If an update that contains changes to the AMD drivers is about to take place it is advisable to move back the AMDRadeonX3000.kext to its default location before the update process. Otherwise the updater writes at least another kext of a different version to its default location or at worst you end up with an undefined state of partially non-matching drivers.
After any system update the folder /System/Library/Extensions has to be checked for the offending kext. Its presence there will lead to e.g. a boot hang on Yosemite and Sierra, an overheating boot-loop in High Sierra.
Escribo en español y traduzco después al Inglés:
Me ocurrió lo mismo. Es necesario saber que, a priori, no se puede instalar un OS superior a High Sierra 10.13.6.
La solución era introducir, a través del teclado, el comando para deshabilitar el chip gráfico pero sin ver nada en pantalla. El comando es el siguiente (una sola línea):
nvram fa4ce28d-b62f-4c99-9cc3-6815686e30f9:gpu-power-prefs=%01%00%00%00
Pero al principio no funcionaba. Tardé en darme cuenta que mi teclado es español y tras reiniciar los caracteres del teclado no corresponden con los caracteres del sistema. Así que con una tabla de correspondencia en un papel introduje el comando considerando sustituir los caracteres -, =, :, ", /, \ y + por las siguientes equivalencias:
= (¿¡) pulsar una sola tecla sin el shift =
: Ñ
“ ¨
/ - es decir para sacar la inclinada de encima del siete pulsamos el - a la izqda de shift-dcho
\ ç es decir la barra raíz de alt+º se consigue con la cedilla ç
y de este modo funcionó.
Actualmente tengo instalados dos SSD:
Uno con High Sierra 10.13.6. Su problema es que no controlo el brillo y si se cae en suspensión pierdo la pantalla con lo que tengo que apagar con el botón I/0 y reiniciar el sistema.
Otro con Catalina mediante la instalación del macOS Catalina Patcher descargado desde https://dosdude1.com/catalina/ Tengo control de brillo y si cae en suspensión no se cuelga. Por contra, el Patcher no es compatible con Chrome por su bajo nivel de seguridad pues tiene el CSRUTIL deshabitado....por lo que debo navegar con Firefox...
Todo esto después de haber leído las dos páginas:
https://gist.github.com/cdleon/d1eff7246a25193304284ecec40445b0
y
https://gist.github.com/cdleon/d16e7743e6f056fedbebc329333d79df
Espero que te sea de ayuda
====================
I write in Spanish and then translate into English:
The same thing happened to me. It is necessary to know that, a priori, you cannot install an OS higher than High Sierra 10.13.6.
The solution was to enter, through the keyboard, the command to disable the graphics chip but without seeing anything on the display screen. The command is as follows (single line):
nvram fa4ce28d-b62f-4c99-9cc3-6815686e30f9:gpu-power-prefs=%01%00%00%00
But at first it didn't work. It took me a while to realize that my keyboard is Spanish and after restarting the keyboard characters do not correspond to the system characters. So with a correspondence table on a paper I entered the command considering replacing the characters -, =, :, ", /, \ and + with the following equivalences:
= (¿¡) press a single key without the shift =
: Ñ
“ ¨
/ - to obtain the slope above the seven, press the - to the left of shift-right
\ ç to obtain, the root bar of alt+º is achieved with the cedilla ç
and this way it worked.
I currently have two SSDs installed:
One with High Sierra 10.13.6. Its problem is that I don't control the brightness and if it goes to sleep I lose the screen so I have to turn it off with the I/0 button and restart the system.
Another with Catalina by installing the macOS Catalina Patcher downloaded from https://dosdude1.com/catalina/
I have brightness control and if it goes to sleep it doesn't hang. On the other hand, the Patcher is not compatible with Chrome due to its low level of security since it has the CSRUTIL disabled...so I have to navigate with Firefox...
All this after having read the two pages:
https://gist.github.com/cdleon/d1eff7246a25193304284ecec40445b0
and
https://gist.github.com/cdleon/d16e7743e6f056fedbebc329333d79df
I hope this helps you