I chose 10 and it proceed to download the packages directly from Apple's servers. In Terminal I change directory to where I download the extracted macadmin-scripts-main.zip and executed is as: macadmin-scripts-main % sudo. Using the installinstallmacos.py python script from GitHub:

Note that I did not completely download it as I already have the installer and no need for the to download it again at this point, however the fact that is was downloading the packages, including the biggest one which was 11.3G in size, I'll assume the script will finish correctly as this script has been available on the Internet and in use for some time now and ifs still being maintained. What I tried next was to use the third-party python script that downloads the various packages directly from Apple's servers and assembles them into the installer app.

I got the same 'Update not found' error message as with the other methods. I then tried using Terminal and the softwareupdate command: sudo softwareupdate -d -fetch-full-installer -full-installer-version 11.0.1 Using a clean install of macOS Big Sur and then attempting to download the macOS Big Sur installer on the running occurrence of it, I was unable to do it using the methods described in the answers by bmike and Nimesh Neema in this thread. How can I get ahold of the installer file? I'm finding that since this Mac is already upgraded, I can't download it again. How can I download the macOS Big Sur installer on a Mac which is already running Big Sur?

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