Can't build due to PostCSS

[bovine3dom]

~/p/site (master|✚1) $ hugo
Start building sites … 
hugo v0.104.3+extended linux/amd64 BuildDate=unknown
Error: Error building site: POSTCSS: failed to transform "css/main.css" (text/css). Check your PostCSS installation; install with "npm install postcss-cli". See https://gohugo.io/hugo-pipes/postcss/: this feature is not available in your current Hugo version, see https://goo.gl/YMrWcn for more information
Total in 79 ms

Ideally the site should be built with a GitHub Action so that this just works automatically and I don't have to worry about reproducibility.