The WindowShade control panel disappeared after MacOS 8. The feature became part of the Appearance control panel at that point. You can customize it on this MacOS 9 machine by going to Apple -> Control Panels -> Appearance and clicking on the Options tab. There you have access to the option "Double-click title bar to collapse windows", an option that lets you use the feature the way it originally worked (before the minimize widget was added to the far right end of the title bar).

WindowShade was amaaaazing. There was something that - for a while, was an OSX equivalent…I want to say ‘ShapeShifter’(?) - but it only worked for versions from like 10.2-10.4.