Download an earlier version of MacOS on a Mac with later OS

When I try to download an earlier version of MacOS on my Mac that has OS Ventura, I get this message. "Install macOS Monterey" cannot be opened from a newer version of MacOS. For more info visit: https://support.apple.com/HT2011372

If I wanted to create a bootable OS on ext drive to install on another Mac how can I obtain a copy? In trying to wipe the Mac ready for sale I have managed to wipe the OS and now get the folder with a ? on start up! I have tried all the Key combinations on Start Up and all result in failure including the revolving world asking for WiFi settings which run for a while then stop.