add_filter( 'get_avatar_url', 'ganti_foto_avatar', 10, 3 );

function ganti_foto_avatar( $url, $id_or_email, $args ) {
    if ( is_numeric( $id_or_email ) ) {
        $user_id = $id_or_email;
    } elseif ( is_string( $id_or_email ) && ( $user = get_user_by( 'email', $id_or_email ) ) ) {
        $user_id = $user->ID;
    } elseif ( is_object( $id_or_email ) && ! empty( $id_or_email->user_id ) ) {
        $user_id = (int) $id_or_email->user_id;
    }

    if ( empty( $user_id ) ) {
        return $url;
    }

    $custom_avatar = rwmb_meta( 'custom_avatar', [ 'object_type' => 'user' ], $user_id );//Sesuaikan 'custom_avatar' dengan ID Single image yang Anda buat.

    if ( ! $custom_avatar ) {
        return $url;
    }

    $url = $custom_avatar['full_url'];

    return $url;
}