To those who have a MacPro3,1 with Penryn cpu and legacy USB, I made a new working fix for patched BaseSystem.dmg to allow (without OpenCore) an USB BigSur Installer booting and installing (only on internal SATA disk), just follow these steps: https://forums.macrumors.com/thread...unsupported-macs-thread.2242172/post-28737950
Even if I already included a patched 0xfff boot.efi, but you might need the @startergo and @Dayo Refind modified , to allow the patched BaseSystem.dmg to boot you can use on refind.conf
Even if I already included a patched 0xfff boot.efi, but you might need the @startergo and @Dayo Refind modified , to allow the patched BaseSystem.dmg to boot you can use on refind.conf
csr_rotate
and csr_values
10,977 or 10,FFF (because those values allow to boot any patched BaseSystem.dmg), moreover their customized Refind version should allow also the bootscreen for non EFI Metal GPU .