add another html tag after li element in wp_nav_menu

When using wp_nav_menu() you can exclude the <ul> tag by setting the items_wrap to only include the list items (%3$s), then you can add your own <li> before or after that, and wrap it with <ul> yourself:

<ul class="footer-links">
    <li>
        <p>copyright C 2021</p>
    </li>

    <?php
    wp_nav_menu( 
        array(
            'menu'           => 'Footer Navigation Menu', 
            'theme_location' => 'top_nav_menu', 
            'items_wrap'     => '%3$s',
        )
    );
    ?>
</ul>