JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://cdn.jsdelivr.net/npm/select2@4.0.13/dist/js/select2.min.js"></script>
<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/select2@4.0.13/dist/css/select2.min.css">
<h2 style="padding:0px;margin:0px">
JSFiddle Example (Fixed & Working)
</h2>
<p style="padding:0px;margin:0px"><em>Using the latest release of select2 (4.0.13)</em></p>
<br/><br/>
<button id="add-cust">Add +</button>
<br/>
<table id="job-customers">
  <thead>
    <th>#</th>
    <th>Customer</th>
  </thead>
  <tbody>
    <tr id="row-customer-1">
      <td>1</td>
      <td id="selcol">
        <select id="sel" class="select2" data-placeholder="Choose">
            <option></option>
            <option value="a">ABC Co. INC</option>
            <option value="b">Mega Enterprises</option>
            <option value="c">Material Supply Co.</option>
            <option value="d">A-Z Tools & Stuff</option>
        </select>
      </td>
    </tr>
  </tbody>
  </table>

CSS

.select2-container {
    min-width: 200px;
    padding: 5px;
}

JavaScript

$(document).ready(function () {
    $(".select2").select2(); //INITIALIZE SELECT2 ELEMENTS ON DOM LOAD
    
    //BUTTON CLICK
    $("#add-cust").click(function () {
    		let table = document.getElementById("job-customers");
				let last_customer = parseInt(table.tBodies[0].rows.length, 10);
				let new_customer = last_customer+1;
      	let row = table.insertRow(-1);
				row.setAttribute('id', 'row-customer-'+new_customer);
				row.setAttribute('class', 'customer');
      	let cell1 = row.insertCell(-1);
				let cell2 = row.insertCell(1); 
        cell1.innerText = new_customer;

        //LOOP ROWS IN TBODY COL2 & DESTROY SELECT2 ELEMENTS
        $("#job-customers").find("tbody td:nth-child(2)").each(function () {
        		$(this).children("select")
            .select2("destroy")
            .end();
        });
        
				//CLONE & APPEND
       	$("#row-customer-" + last_customer + " td:nth-child(2)")
           .children("select").clone()
           .attr('id', 'sel-'+new_customer) //UPDATE ID USING ROW/CUST #
           .appendTo(cell2);
           
        //RE-INITIALIZE SELECT2 ELEMNTS
				$(".select2").select2();
    });
});