Back-to-Top Anchor Appended to Post Content

<?php
add_filter( 'the_content', 'scseed_back_to_top_anchor' );
function scseed_back_to_top_anchor( $content ) {
    if ( ! is_singular() || ! in_the_loop() ) {
        return $content;
    }
    $link = '<p class="scseed-back-to-top"><a href="#top">'
        . esc_html__( '&#8593; Back to top', 'textdomain' )
        . '</a></p>';
    return $content . $link;
}