You will notice the output of the command reads Installing X%.
Don’t worry, it’s not installing the update on your Mac. All it’s doing is downloading the installer to your Applications folder.
Wait for the progress to reach 100% and the output to say Install finished successfully, then you should see the Install macOS Big Sur app appear in Applications.
You can now use the Install macOS Big Sur app to upgrade your Mac’s operating system or use it to create removable media to upgrade another Mac. Check out the following tutorials to learn how to create a bootable DVD or USB Flash Drive.