As stated above we can extract the NvramSmi driver from an older BIOS and the replace it in the latest one. I believe most our boards from this era are no longer being supported but the latest firmwares do have microcode to patch vulnerabilities like Spectre, meltdown, etc. It would be ideal to go this route and it's not that hard and working nvram is great!
I'm guessing another way would be to flash back to old BIOS where native nvram is working and upgrade/install Big Sur and then flash the latest after. You could save your BIOS profile if available that way you won't have to set everything back up. If this is also the case for incremental updates, sounds like a nightmare.
How (I chose to fix)
Replacing the NvramSmi driver made the most sense and it was relatively easy. I am no expert and you know the responsibility I take in anyone trying this shit and failing, ZERO.
To find a BIOS version before the whitelist was added to the NvramSmi driver I used the dates from the link in Vit9696's quotes. User 314TeR said his ASUS Maximus VII Impact nvram broke after 0412 which was released 2014/10/17 and worked with 0217 released 2017/07/28. To me anything after 2014/10/17 will have added the whitelist.
So with my board I downloaded version 1104.
Download UEFITool 0.26.0 as the latest versions won't let you rebuild/replace.
Download latest BIOS and one without whitelist.
Load older BIOS in UEFI tool, my case 1104. Search with text nvramsmi and extract as is, the file section. Like below. Save the ffs, name it whatever and close out we are done here.
楼主: 藍凌
