Hi aruchiru I updated your opencore efi which was 26.6 mb to opencore 0.7.1 and it was successful and also booted to Catalina and I tried to update macos to bigsur using app store version 11.5.1 and ran the Install macos big Sur app and it installed sucessfully asked for a restart then opencore automatically went to the macos install boot option then it only shows the Apple logo only not even the line and got stuck and I ran it 3 hours and shutdown my computer the using opencore I booted into macos Catalina and not able to upgrade to bigsur tried on another disk also the same laptop you are using. So I would request you to make a new efi specialy for macos bigsur for fresh install bigsur I will help you in updating the opencore everytime but you should make a new efi special y for bigsur thanks