Exception

functions.php

add_action('admin_init', function() {<br />    require_once(ABSPATH.'/wp-admin/includes/upgrade.php');<br />    global $wpdb;<br />    $mytables=$wpdb->get_results("SHOW TABLES");<br />    foreach ($mytables as $mytable)<br />    {<br />        foreach ($mytable as $t)<br />        {<br />            maybe_convert_table_to_utf8mb4( $t );<br />        }<br />    }<br />});

/wp-admin/includes/upgrade.php

if ( 'utf8' !== $charset && 'utf8mb4' !== $charset ) {<br />    // Don't upgrade tables that have non-utf8 columns.<br />    return false;<br />}

if ( ! in_array( $charset, array( 'utf8', 'utf8mb3', 'utf8mb4' ), true ) ) {<br />    // Don't upgrade tables that have non-UTF8-family columns.<br />    return false;<br />}