Disabling CSM | Opencore | No Boot Picker, No Verbose

I have recently swapped my previous Nvidia GPU GTX 960 by an Radeon RX 570, which allowed me to boot with CSM disabled. The Nvidia did not allow to boot with CSM disabled: three short beeps from MOBO meaning no GPU detected unable to choose boot device and unable to enter into BIOS setup, the only way out was to clear CMOS (although sometimes waiting less than a minute the system booted).

Currently with the new GPU there is not rejection from the MOBO with CSM disabled, and I...

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