Including plain text URL to post on same site is converting the URL to an embed

To prevent WordPress from automatically turning URLs into embeds, you can disable oEmbed for internal links. One way to do this is by adding a small function to your theme’s functions.php file or a site-specific plugin. This function would stop WordPress from treating your own site’s URLs as oEmbed sources.

Try this:

function disable_self_pingbacks( &$links ) {
    foreach ( $links as $l => $link ) {
            unset($links[$l]);
    }
}

add_action( 'pre_ping', 'disable_self_pingbacks' );