Ok, I have created a new EFI folder based on the Dortania Haswell-E guide for you to try.
It has been created using OC 0.6.7. The OC folder is quite a bit different from your previous one, as I have included a number of additional kexts, SSDT's and config.plist entries that are specific to your Haswell-E system and your use of an RX580 Graphics card. Screenshot of the OC folder is shown below:
This OC setup uses the OC GUI not the picker list.
It uses the iMacPro1,1 SMBIOS.
Remember to Clear and then Reset the NVRAM when you boot this folder, the two icons will be shown on the OC boot screen. You need to do this so any old Nvram settings are removed and you start with a clean slate.
See if this works any better than your previous EFI folder.
Ok, good to know. I have not used that boot argument since last setting up my AMD FX3850, FX990 hack!
Do you have 'Above 4G' enabled in your bios?
Do you have 'VT-d' disabled in your bios?
Do you have 'CFG-Lock' disabled in your bios?
Can you post a copy of your ACPI tables from this system. You need to either boot in to Clover and press the F4 key while on the boot screen. Or boot in to Mojave or Catalina desktop, and use Hackintool App > Utilities tab and select the icon to dump the ACPI tables to your desktop.
There are lots of other posts going back to the initial release of Big Sur's Public Beta saying similar things.
There have been a few people who have used setups from Chinese X99 boards to get Big Sur installed. But this method can be a bit hit and miss.
The main way people have got around the broken NVRAM issue has been to install Big Sur on a spare drive in a real Mac or another Hack, but one with working NVRAM and then to transfer the Big Sur drive to their X99 system. Using the OC folder that worked in macOS Catalina.
I am working through some adaptations to an OC Config.plist, basing it on some previous settings from a couple of X99 Clover folders I created previously. This is a bit tedious but I should have all the rename patches etc. added to the OC config tomorrow.
I appreciate you providing a copy of the ACPI tables, this has enabled me to see which devices are present in the DSDT.aml and also to generate some custom SSDT's for your system using Corpnewt's SSDTTime script. These are attached in the Results folder below.
These SSDT's and patches will eventually need to be added to your OC setup, once I have finished with the rename patches. They may need tweaking to work with the CPU and other device renames.