How to remove inline styling of copied content from webpage using jQuery?

For better readability I have only used few lines of code from what you have added in your question.

If you can use regex to replace style from the html content. Here is a helpful piece of code, you can try this out:

var str = '<span style="color: rgb(34, 34, 34); font-family: sans-serif; font-size: 14px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400;">In 1896 and named after its inventor, </span><a href="https://en.wikipedia.org/wiki/Georges-Fernand_Widal" title="Georges-Fernand Widal" style="color: rgb(11, 0, 128); background-image: none; background-position: initial; background-color: rgb(255, 255, 255); font-family: sans-serif; font-size: 14px; font-style: normal; font-variant-ligatures: normal; fot-variant-caps: normal; font-weight: 400;">Georges-Fernand Widal</a>';
ret = str.replace(/style=".*?"/gm,'');
console.log(ret);

Anything inside style="..." will be removed by using this.

g in regex is used for global search in given string m in regex for multi-line search

Answer Updated:

If you need to Decode the above code as HTML format, you can see below section:

var str = '<span style="color: rgb(34, 34, 34); font-family: sans-serif; font-size: 14px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400;">In 1896 and named after its inventor, </span><a href="https://en.wikipedia.org/wiki/Georges-Fernand_Widal" title="Georges-Fernand Widal" style="color: rgb(11, 0, 128); background-image: none; background-position: initial; background-color: rgb(255, 255, 255); font-family: sans-serif; font-size: 14px; font-style: normal; font-variant-ligatures: normal; fot-variant-caps: normal; font-weight: 400;">Georges-Fernand Widal</a>';
ret = str.replace(/style=".*?"/gm, '');
// console.log(ret);

var parser = new DOMParser;
var dom = parser.parseFromString(
  '<!doctype html><body>' + ret,
  'text/html');
var decodedString = dom.body.textContent;
// console.log(decodedString);

var actualHTML = $('<textarea />').html(decodedString).text();
console.log(actualHTML);
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>