I don't ever use the three buttons on the top left corner and instead use hotkeys for managing my apps. I want the traffic lights disable to save space in some apps.
Christmas Tree https://forums.macrumors.com/threads/i-made-a-christmas-tree-for-your-mac.2373022/I cannot recall any macOS app not having a title bar.
SIMBL is not working on current macOS versions https://github.com/w0lfschild/mySIMBLYou could probably disable SIP and use a SIMBL plugin to do the equivalent of setting titleless and full-content for the NSWindow on all apps. This might break some applications that are sensitive to layout
There's apparently a beta for macforge,