Go to
BarryKN's GitHub, download his latest micropatcher (ver 0.2.1 today). Read his README file. All the steps are expertly given.
Prepare your USB just as if you have a supported Mac (lots of sites give these instructions):
1. Download copy of the macOS Big Sur InstallAssistant.pkg. For BigSur Beta5 the link was:
http://swcdn.apple.com/content/down...767kq54klqanh09mrcted2kw/InstallAssistant.pkg
Run the pkg in Downloads to place Install macOS Big Sur Beta in Applications.
2. Create bootable USB of at least 16GB using DiskUtility. Format as MacOS Extended (Journaled) with GUID Partition Map. I named the stick MacOS.
3. From Terminal type: (note: in this step you are creating your bootable USB installer)
sudo /Applications/Install\ macOS\ Big\ Sur\ Beta.app/Contents/Resources/createinstallmedia --volume /Volumes/MacOS
Follow the screen’s instructions. After several minutes Terminal will say the Install macOS Big Sur Beta USB was created.
Now follow BarryKN's instructions and let us know if you are successful -- as explained in several posts just above this, no one has been able to get past the gray screen lock.