The reason is that while I was installing it, I missed one line and got confused about whether I need to complete instructions on the rest of the page(manual installation).

The documentation of the "Installation Script" procedure is here ..

https://docs.searxng.org/admin/installation-scripts.html

At the end there is a hint about HTTP proxy setup

Not sure how we can improve it ..

Also, I suggest including selection of HTTP server (or not installing any) to the installation script, instead of making it a separate article/instructions.

Installation of SearXNG services and HTTP server are different tasks and I think we should not mix up these both tasks which each other.. most maintainers already have a HTTP setup and might be confused if they have to decide to install a HTTP server while installing SearXNG services.