At some point you may wish to perform a full clean install of your macOS, which maybe Big Sur or an older system version like Catalina.
For most people a handy utility like DiskMaker X is an useful option, however not working anymore and never will be for Big Sur.
Apple increased security levels in Big Sur which makes it harder or impossible for third party software to enter parts of the system. Below a manual creation is described in order to create a bootable Big Sur installer:
- Download: macOS Big Sur, macOS Catalina, macOS Mojave, or macOS High Sierra
These download to your Applications folder as an app named Install macOS [version name]. If the installer opens after downloading, quit it without continuing installation. To get the correct installer, download from a Mac that is using macOS Sierra 10.12.5 or later, or El Capitan 10.11.6. Enterprise administrators, please download from Apple, not a locally hosted software-update server.
- Download: OS X El Capitan
This downloads as a disk image named InstallMacOSX.dmg. On a Mac that is compatible with El Capitan, open the disk image and run the installer within, named InstallMacOSX.pkg. It installs an app named Install OS X El Capitan into your Applications folder. You will create the bootable installer from this app, not from the disk image or .pkg installer.