How to download full macOS installer, instead of the 'stub'?

Can someone give me detailed instructions for this? For some reason, the instructions on this page no longer work, as I'm only getting the approx. 50 MB 'stub' file instead of the full installer. I found another thread here that describes using the softwareupdate command in Terminal, but the commands they shared are incomplete, or at least they don't work for me in the version of Terminal included in Sequoia. All I get is something similar to a man page.

This is really annoying, as the instructions listed on the page linked above used to work, and now they don't...