I think Windows was built in house but on top of DOS which Bill Gates bought off someone
Yeah, it started its life as “Quick And Dirty Operating System” (don’t know, why they renamed it) and even that was basically a ripoff of CP/M: https://en.wikipedia.org/wiki/86-DOS
I guess, you can say that they did put in own effort into developing the windowing system. I wouldn’t want to call that “innovating”, since they were late to the party, but I guess, that would be moving the goal posts here…