I have found several guides on how to put the installer on external media using this command:
sudo /Applications/Install\ macOS\ Mojave.app/Contents/Resources/createinstallmedia --volume /Volumes/Untitled/ --nointeraction
However, when I run that command I get the error:
To use this tool, you must download the macOS installer application on
a Mac with 10.12.5 or later, or El Capitan 10.11.6. For more
information, please see the following:
https://support.apple.com/kb/HT201372.
I'm running 10.11.6, but when I follow that support article I get led in a circle – back to the App Store, which downloaded an 11 MB installer which led to the above error in the first place.
The only other thing I find is some third party web site that I am supposed to trust, to install their own tool to do the download. I am not going to install and trust such third party software. All I need to do is download the full version of the installer. Surely Apple must provide this somehow, since their own command is referring me to their own documentation (which strangely doesn't tell me how to download the whole installer in a way that works!)
How do I get the full installer?
Note: This may seem like a duplicate of this question which is marked as a duplicate of this question. But all of the answers for those question either don't work (lead me in a circle back to the App Store which downloads a tiny installer even after I delete it and try again) or refer me to a third piece of software that I'm not going to trust.
Best Answer
To perform a clean install, try using Internet recovery.