Apple official procedure for creating a Big Sur external boot drive on an M1 running Monterey?

I have an M1 Mini, currently running Monterey, but I would like to be able to boot into Big Sur, the earliest OS I can use on it. In researching how to create an external boot drive for an M1 with an older OS on it, I have run into no information where I expected to find it, useless information, and outright wrong information, coming from formerly reliable sources: this forum, AppleCare, and The Genius Bar at the Apple Store. Is there any official description how to do that that someone can link me to? A choice of startup disks is still possible through System Preferences. Is it possible, or isn't it?