Note about OpenVariableRuntimeDxe.efi
Old machines with legacy BIOS (i.e. machines which do not have UEFI compatible firmware) can install OpenDuet from the Utilities/LegacyBoot folder of OpenCore. OpenDuet behaves as a compatibility layer prior to OpenCore, to provide UEFI on machines which previously lacked it. It includes in-memory emulation of NVRAM (which is normally present in hardware, on all UEFI compatible machines). This new OpenVariableRuntimeDxe driver allows the use of in-memory emulated NVRAM with OpenCore, separately from OpenDuet.
OpenVariableRuntimeDxe not only brings emulated NVRAM to OpenCore, it also adds some improvements in functionality even for OpenDuet users (correct handling of NVRAM reset and CTRL+Enter). Importantly, in bringing emulated NVRAM to OpenCore, OpenVariableRuntimeDxe opens the possibility of using emulated NVRAM instead of original hardware NVRAM on UEFI machines with fragile hardware NVRAM implementations (for instance, where excessive NVRAM usage can eventually cause bricking, such as on the MacPro 4,1 and 5,1).