The entire page is not visible due to the presence of the .d-none .d-xl-block classes on the div you wish to view. These classes only make the div visible on extra-large screen devices.
To resolve this issue, simply remove those classes and update the code as follows:
<div class="col-xl-2 bd-toc disapear1">
I have corrected the inline-style closing tag in the footer as well. Here is the updated HTML snippet:
<!DOCTYPE html>
<html lang="en">
<head>
<title>CONFT</title>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.5.2/css/bootstrap.min.css">
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.5.1/jquery.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.16.0/umd/popper.min.js"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.5.2/js/bootstrap.min.js"></script>
<link rel="shortcut icon" href="images/logo_tab_icon.png" type="image/x-icon">
<style>
/* CSS Styles */
</style>
<script>
/* JavaScript Code */
</script>
</head>
<body data-spy="scroll" data-target="#myScrollspy" data-offset="1">
// Navbar section goes here
<div class="col-xl-2 bd-toc disapear1">
// Content within the col-xl-2 div
</div>
// Footer section goes here
</body>
</html>
p.s. Please note that the first section may be hidden behind the navbar. You can add a margin-top to prevent this overlap.