Sorry, but a MacOS that doesn’t have animated wallpapers still can be said to ‘behave itself’.
/System/Library/Frameworks/ScreenSaver.framework/Resources/ScreenSaverEngine.app/Contents/MacOS/ScreenSaverEngine -background
https://osxdaily.com/2011/01/22/set-a-screensaver-as-your-de...I used to do this once in a while, back in PowerPC days. Twenty years ago, it was amusing.