JSFiddle - React, Tailwind, and code Playground

HTML

<form>
    <input type="checkbox" id="cb1" />
    <label for="cb1">Cb 1</label><br/>    
    <input type="checkbox" id="cb2" />
    <label for="cb2">Cb 2</label><br/>    
    <input type="checkbox" id="cb3" />
    <label for="cb3">Cb 3</label><br/>    
    <input type="checkbox" id="cb4" />
    <label for="cb4">Cb 4</label><br/>    
</form>

<div id="num">0</div>

JavaScript

var $allCb = $("input[type=checkbox]");

$("input[type=checkbox]").change(checkMaxNumber);

function checkMaxNumber() {
    var $cb = $(this),
        nb = $("input[type=checkbox]:checked").length;
        $("input[type=checkbox]:not(:checked)").prop("disabled", nb >= 2);
    
    $("#num").text(nb);
}