There was no need to downgrade BIOS if you were on A20 which is perfectly Ok to run with. The steps to follow are the same whether you use Clover or OpenCore. You may refer to the guides for previous versions if need be.
My guide is for any 11.x Big Sur version; I've amended the version line to that effect. At the time of writing, there was uncertainty with regards to the new version numbering adopted by Apple and it was not known whiter Big Sur would remain 11.0.x or turn to 11.x.x
Only need the compiled SSDT.aml but you'll have to rename it as SSDT-PM.aml as that's what the config.plist is expecting. It's hardcoded in OC. If you want it to read SSDT.aml, then rename it in the config file.
or add it and disable SSDT-PM.aml
if your processor is anything other than i7-3540M, you'll need to disable SSDT-PM.aml or generate one and replace it with the same name in ACPI folder.
11.0.x is the version of MacOS. The bootpack can be found at the bottom of the guide under
1) 11.0 USB installer creation
uncompress the following E6230 Big Sur OpenCore pack and copy the EFI folder to the mounted EFI partition: