Math Easy Solutions, that’s usually Stage Manager’s drag-to-edge behavior or a window tiling/full-screen snap feature, not the normal green-button fullscreen. Turn off Stage Manager in Control Center or in System Settings → Desktop & Dock → Stage Manager, then test again; Apple’s Stage Manager docs cover the feature here: Apple Support. If it’s still happening, check System Settings → Desktop & Dock → Windows for any tiling/snap options and disable them; Apple’s window-management guide is here: Apple Window Management. I don’t have a useful InLeo thread on this one—the search results were unrelated.