this efi works to install and load bigsur but the OC is really old ive tried the updater but i get oc: grabbed zero system-id for sb this is not allowed maybe this will help someone....i hope
as the file size was too big i could only get the kext's and bits, you need open core 0.7.2 and this booted BigSur 10.7.10 this includes the plist and files i couldnt get the TP to work properly but it sees battery wifi etc my bios is 1.42.0
OC072.zip
ive found an Open Core updater used that and then open this plist and look for secureboot and it might say its setting is default i chose "disabled" and it now boots BigSur again just need upto date Kext now