Add filter for specific post type only

There’s a couple ways you could handle this.

Option 1 Check the global $post object

Inside your filter you may be able to check the current $post object or other Conditional Tags for a specific type.

function my_super_filer_function6( $args ) {

    global $post;

    /* Check against the current post object */
    if( empty( $post ) || 'post_type_here' !== $post->post_type ) {
        return $args;
    }

    /* Check conditional tags */
    if( ! ( is_post_type_archive( 'post_type_here' ) || is_singular( 'post_type_here' ) ) ) {
        return $args;
    }

    /* ... */

}

Option 2 Add the hook via template_redirect or an early hook

You may be able to add the hook via an earlier action hook:

function wpse350295_init() {

    if( is_post_type_archive( 'post_type_here' ) || is_singular( 'post_type_here' ) ) {
        add_filter( 'listing/grid/posts-query-args', 'my_super_filer_function6' );
    }

}
add_action( 'template_redirect', 'wpse350295_init' );

Option 3 Use the args

You may be able to check the passed args for a post_type and return early if the post type does not match what is expected:

function my_super_filer_function6($query_args){

    if( 'post_type' !== $query_args->get( 'post_type' ) ) {
        return $query_args
    }

    /* ... */

}

This is of course assuming what is being passed is a WP_Query object. You would need to do some due diligence to figure out what the passed variable holds and if a post type can be discerned from it.