how to do a clean install
How to do a clean install of big sur.
iMac 27″, macOS 10.15
Question marked as
One can do this via Internet Recovery ( not suggested ) OR and Better is download the Full Big Sur on a compatible computer and stop there. Do not allow it to run. If it tries, close the installer. In Applications folder will be a New App Install Big Sur. Copy this to a good external drive for safe keeping. Run a TM Backup and also a Bootable Clone or two to each there own External Drive. Have 16 GB USB drive attached, Format as HFS ( Journaled ) and GUID Partition. Name it Untitled. Open Terminal and run the command
sudo /Applications/Install\ macOS\ Big\ Sur.app/Contents/Resources/createinstallmedia --volume /Volumes/Untitled --
/Applications/Install\ macOS\ Big\ Sur.app
Once complete shutdown computer. Restart and immediately press Option key. Choose to boot from the USB Installer. Use Utilities >> Disk Utiities and point it to the Top Most internal drive name ( Like Apple SSD xxxx ) . Format it as APFS and GUID Partition. This will destroy all on the drive. Back out of Utilities and launch Install Big Sur