It was tried out per window, but changed:

https://milos.fyi/blog/fitts-law-why-the-menu-bar-is-at-the-...

In this video Bill explains why he moved it. At 28 min he says: "…and if the window is near the bottom, how are you going to show all the choices? Well, I tried moving the menus to the top of the screen."

https://www.cs.cmu.edu/~bam/uicourse/05440inter2019/Bill-Atk...