I think a better title would be "Designing Icons for Material Design". The guide comes over as very opinionated in places, which doesn't match all past or even contemporary uses of icons - but the guidelines make sense as part of Google's Material Design system.
+1 to the title being wrong.
>material.io
I can't say I'd ever consider "Material Design" to be an authority on what good iconography or website design should look like. It's always felt second-rate.
So bland. Call me nostalgic but I really miss the diversity (but consistency) of the Windows XP-era of icon design.