While it definitely works without Ruby knowledge, I found it rather un-fun to maintain a Ruby environment. And I felt a bit locked out of customizing it.
For those with some JS familiarity who want a static but highly customizable site, I recommend 11ty or Astro.build as a modern-day Middleman alternatives. They are written in javascript top to bottom, but importantly do not presume you are interested in shipping a ton of heavy javascript to the client the way Nextjs does.
Hugo, based on Go, is really fast and reasonably customizable. I could just never wrap my head around the syntax of go templates.