Opencore can now boot to the installer for those who have been trying to install Big Sur.

Apparently the Opencore developers have resolved the booting into installer issues with the latest commit to their boot loader.

You'll need to download the latest commit (not one of the release versions) https://github.com/acidanthera/OpenCorePkg

I personally have not tried it yet but others have reported success on InsanelyMac forums. I wanted to get this out there as there's no requirement to use VMs or downloaded images to install Big Sur.