bash has been available on Windows since at least before the mid '90s.

Yes I remember using cygwin back in 2004ish to provide bash when I had to use a windows pc at work (very briefly)

I was a co-op at a company in the 90s that specialzed in mechanical simulation of virtual prototypes. The software was primarily used on Unix (most of us used SGI boxes) but there was also a Windows port for smaller jobs and laptop use and (at least the dev environment) was all built on Cygwin.