Fatal error: Class ‘wp_bootstrap_navwalker’ not found in /

Solution:

The next step is to create the WP_Bootstrap_Navwalker.php and include it. Put the following line into functions.php: file require_once(get_template_directory() . "/inc/wp-bootstrap-navwalker.php");

This assumes that the file is in an /inc folder. If the site now runs without error, the final step is to add the 'walker' => new WP_Bootstrap_Navwalker() line to the wp_nav_menu call.

More info: https://github.com/wp-bootstrap/wp-bootstrap-navwalker

Try to update your code here:

<?php
    wp_nav_menu( array(
        'menu'              => 'primary',
        'theme_location'    => 'primary',
        'depth'             => 2,
        'container'         => 'div',
        'container_class'   => 'collapse navbar-collapse',
        'container_id'      => 'bs-example-navbar-collapse-1',
        'menu_class'        => 'nav navbar-nav',
        'fallback_cb'       => 'WP_Bootstrap_Navwalker::fallback',
        'walker'            => new WP_Bootstrap_Navwalker()
        ));
?>

I hope it will be helpful for you