Consider Nuxt instead of Vuepress/Vitepress. If you want the built-in theme in Vitepress, it's great, but if you want to make your own, using Nuxt with the Content plugin is probably better. I found the strong separation between theme and content to be too great, and if I have a docs SSG site using Vitepress and a webapp SSR site using Nuxt, I can't share themes easily anyway.

At least that was my conclusion starting with Vitepress, and ending up with Nuxt 3.

https://nuxt.com/

https://vitepress.dev/ (they haven't decided if they are going to replace Vuepress or not: https://github.com/vuejs/vitepress/discussions/548)