Apple Silicon will allow custom kernels(Linux) to be enrolled in to the secure boot policy(a change from x86 macs)

Lounge
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State here in GNU Grub about Arm
there no legacy , or bios mode on theses motherboards

in case for Apple , if there is always any /boot/efi means a Secureboot or shim used

if clover is being rewrited for more openboot , there is a reason

as all hardware Apple will be blocked in time on version Ios ( 6 to 8 years ) ,
only linux ( or you want to fight to get a BSD ) can be up to date.

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