Programmatically modify WooCommerce product description

/**
 * Modifies product description.
 *
 * @see https://wpcodebook.com/woocommerce-programmatically-modify-product-description/
 */
add_filter( 'the_content', function ( $content ) {
	global $product;
	if (
		! is_product() ||
		! $product
	) {
		return $content;
	}
	return $content .
		'<p>' .
			esc_html__( 'My custom description.' ) .
		'</p>';
} );