Sorry, that was my best go at creating an OC folder for an X99 board. I used a Clover folder that I created for another member on this site, I can't think of anything else we could try.
You may need to install Big Sur on your drive in a different system, real Mac or another hack (something newer than a Haswell would work as they tend to have functional NVRAM) and then see about transferring the drive to your X99 system. This seems to be the best option for a lot of X99 system owners who want to upgrade to Big Sur. As it usually gets them over the NVRAM failure and other boot issues.