vue-windicss-preprocess has been archived by the owner.

[multics]

As the owner mentioned here.

This package will be archived, we will give up support for it, please switch your project to windicss-webpack-plugin.

So the guide might to update to catch up the decision.

[antfu]

We are actively working on a new docs site which will be live soon
https://next.windicss.org/guide/installation.html