

Chicago95 XFCE on Debian is my daily driver. Having been a Windows 2000 fanboy, it makes me feel right at home.
The Raleigh GTK theme ported to GTK 3 on XFCE is also a quick and dirty way to get a 90s-esque look: https://github.com/thesquash/gtk-theme-raleigh
For an entire distro, there’s Hot Dog Linux: https://github.com/arthurchoung/HOTDOG
Maybe a bit niche, but in higher level math courses, instructional material often seems out-of-touch, written by professionals for professionals. Inconsistent notation between authors and unexplained symbols in equations are also royal pains in the ass.