Windows Aero did work, or at least the Windows 7 incarnation of it.

Wasn't it a bastardized watered down version that cached the elements behind it and still gave a performance hit?

They seem to be running into the same issues and didn't take the learned lessons with them

It was still ugly, but it did kinda work because it only affected the window chrome, and it could be set to opaque with an easy-to-find setting.

On macOS the checkbox for "Reduce transparency" is hidden away in the Accessibility settings panel which is the last place I'd look for configuring the desktop theme.