where do I get an older Mac OS?

See: How to get old versions of macOS - Apple Support

Apple should really update this article. Downgrading from Monterey and using this article for reference will lead to confusion.

That article isn’t meant for people Downgrading. I don’t think they offer any advice to people who don’t wish to use the most current OS, when possible.

If the computer came New with Big Sur installed - this computer can not be used to download an Older version of macOS.

The " Apple Licence of Use Agreement " prohibits is action.