JSFiddle - React, Tailwind, and code Playground

JavaScript

var html = '<body> \
<span class="Forum"><div align="center"></div></span><br /> \
<span class="Topic">Text</span><br /> \
   <hr /> \
  <b>Text</b> Text<br /> \
  <hr width=95% class="sep"/> \
  Text<a href="Text" target="_blank">Text</a> \
   <hr /> \
  <b>Text</b> -Text<br /> \
  <hr width=95% class="sep"/> \
 **Text what i need.**\
   <hr />';
    
var div = document.createElement("div");
div.innerHTML = html;
var hrs = div.getElementsByTagName("hr");

for (var i = 0; i < hrs.length; i++) {
    if (hrs[i].className == "sep") {
        document.body.innerHTML = hrs[i].nextSibling.nodeValue;
        break;
    }
}