Thank you for this.
The instructions on here are different from what it says on Ubuntu's official website. And apparently in macOS Monterey, you can no longer do it that way.
The in this article you liked, it appears to be a little too complicated for me to try it because the risk of me breaking something is already high enough, and I can't afford to do that. I don't have a spare computer either.
I have, however, flashed a Linux Distro on to a USB drive, and it's ready to install. But the old simple system no longer works the way it has been.