Is there any way which does not remove Specific Html tags from the redactor editor using striptags only?
You can simply use striptags filter which removes all HTML tags. But if you want an html tag to be not removed by striptags so you can pass it as argument, then It removes other tags except the ones you pass in.
In other words, if you don’t  want to remove  tag, just use it in this way:
{{entry.content|striptags('&lt;strong&gt;') | raw }}