Can you please check that the machine boots with just grub without shim.
Aka, replace /EFI/Boot/BOOTX64.efi & /ef/ubuntu/shimx64.efi files wtih /efi/ubuntu/grubx64.efi => this could possibly be a workaround, given that secureboot is not possible on Mac platforms.
Can you please check that the machine boots with just grub without shim.
Aka, replace /EFI/Boot/ BOOTX64. efi & /ef/ubuntu/ shimx64. efi files wtih /efi/ubuntu/ grubx64. efi => this could possibly be a workaround, given that secureboot is not possible on Mac platforms.