I’m talking about the System 7/8/9 days of macOS. I really like the aesthetic and workflow in the older macOS versions (call me a masochist) and I’m hoping if someone knows of something that already exists. I know there are plenty of skins/themes that hearken back to Windows 95/98, but most of what you find online when you look for “Linux like macOS 9” is things that make it look like modern macOS.
Look into GNUstep and related projects maybe? I’m not sure how close it is to pre-NS Mac (that was OS X iirc?) but it might be close enough.