According to the Dortania guide, before updating OpenCore to 0.6.6, you should set these in config.plist:
Then you have to reset NVRAM on your OpenCore menu. You have to press the Space key to show the option, or set
False in config.plist.
After booting to macOS again, update OpenCore to 0.6.6 and set
MaxBIOSVersion (exclusive for legacy Macs) to
True in config.plist. I strongly recommend updating OpenCore to 0.6.6 before updating macOS to 11.2 for Macs.
Besides, the latest OpenCore menu is now more genuine.