[Existenceblinks]

Why backend of web development is narrow down to nodejs server? How about people who use Rust/Python/Ruby/Elixir/PHP?

[SkyPuncher]

It's not. If you're building a backend heavy use-case, there are plenty of good options.

Gatsby is geared towards building web pages, not web applications. If you're implementing Gatsby, you're building essentially HTML pages, possibly with some JS functionality.

[Existenceblinks]

It's interesting to me to explore this type of application that is interactive web page, but not web applications

Usually, the more interaction, the more likely it's application. The more it's just a page, the more it should be just HTML.