If you need to use CDATA in feed, you may need to replace symbols with HTML codes, e.g.:

This will be outputted in your feed something like:

<![CDATA[Some Product Title]]>

If you need to include shortcode in tags double quotes, use:

This will be outputted in your feed something like:

<item id="123"></item>

HTML entities are replaced in all (header, footer, item) fields, so:

will be outputted in your feed as:

<item date="2018-09-04 12:42:57">

If you have some specific requirements, you can also create your custom shortcodes to be used in feeds. For example try putting this to your (child)
theme’s functions.php file:

add_shortcode( 'alg_product_price_multiplied_by_stock', 'alg_product_price_multiplied_by_stock' );
if ( ! function_exists( 'alg_product_price_multiplied_by_stock' ) ) {
    function alg_product_price_multiplied_by_stock( $atts ) {
        $product_id = get_the_ID();
        $product    = wc_get_product( $product_id );
        return ( ! $product->is_in_stock() ? 0 : $product->get_price() * $product->get_stock_quantity() );
    }
}

Now you can use it in your feed like:

<stock_price>[alg_product_price_multiplied_by_stock]</stock_price>