The diagrams were done with monodraw - https://monodraw.helftone.com/

Second that these diagrams look really nice and clean- does anyone happen to know if there's an alternative that isn't Mac only?

Have a look at draw.io (https://about.draw.io/features/) which can make a lot of fantastic diagrams. Be sure to look at the "More shapes..." options and choose the libraries that are of interest to you. Free and open-source.

Yeah been using Monodraw since it came out - great application and the few times I've wanted new features the devs have added them!

I've been using Monodraw ever since I started reading brandur's blog, falling in love with his diagrams.