Shortcode contents are not rendered on the page during Hugo Static website

I am quite new to Hugo and trying to understand it through documentation and other things. I am creating a simple shortcode which I would like to include within my page but for some reason the shortcode is not rendered within my page at all.

Following is my shortcode in: layouts\shortcodes\plain.html:

{{ .Page.File.Ext }}
{{ . }}
{{ .Get "title" }}
{{ .Get "linkTitle" }}

<div>
    {{ .Inner }}
</div>

Following is my content which I want to add to my HTML page: \content\en\_index.html:

+++
title = "Home-Test"
linkTitle = "Home-Test"

+++

{{< plain >}}
    <h1>HELLO FROM BLOCKS SHORTCODES</h1>
{{< /plain >}}

Following is my index.html from baseof layouts\_default\baseof.html:

<!doctype html>
<html lang="{{ .Site.Language.Lang }}" class="no-js">
  <head>
    {{ partial "head.html" . }}
  </head> 
  <body>
    {{ partial "loader.html" . }}
    <header>
      {{ partial "navbar.html" . }}
    </header>
    <main>
      {{ block "plain" . }}{{ end }}
    </main>
    <footer>
      {{ partial "footer.html" . }}
    </footer>
    {{ partialCached "scripts.html" . }}
  </body>
</html>

I would expect my content provided <h1>HELLO FROM BLOCKS SHORTCODES</h1> should be displayed on the HTML page rendered by the Hugo but its not displayed. Can someone please correct me what am I doing wrong here?

The short version is that you’re mixing 2 concepts: Shortcodes and blocks.