Startup Disk wont appears (Downgrade To High Sierra)

[rjaffier]

Hey guys,

im running on a mid-2012 macbook pro retina (os catalina) and i want to make a downgrade (to high sierra) but the bootable pendrive wont appears on Startup Disk options.
to get more complicated, since i bought this mac i never set a firmware password but the lock appears. so, when i make some command (like the recovery mode - cmmd + R) asks for the firmware password.

is there a way to set the startup disk to bootable pendrive on terminal without needs the efi pass?


(choose downgrade to high sierra for the video editing apps and the cuda driver support)

 

[rjaffier]

tried to erase the hd but failed (-69877)

 

[diegodp]

Up for this post!
I've the same problem: when I try to downgrade from Catalina to HSierra, any USB Boot disk I've doesn't work on boot.

How can I solve?

 

[Fishrrman]

"to get more complicated, since i bought this mac i never set a firmware password but the lock appears. so, when i make some command (like the recovery mode - cmmd + R) asks for the firmware password."

Did you buy a used Mac?
If you did... and if the previous owner set a firmware password... you're pretty much out of luck.
Apple won't reset it without PROOF of ownership (original sales receipt), and you don't have that.