How to apply discount on variable and single products, based on cart quantity and product attribute in WooCommerce?

I am trying to apply a percentage discount based on quantity of products with a specific product attribute, in cart.

More precisely my goal is to apply 15% discount on orders of minimum 6 products with the attribute flaske.

I have managed to achieve this for variable products with variation attributes set, but I can't seem to target the single/simple products.

My code so far (borrowed from Condition for Quantity and Price for Woocommerce):

// Discount based on product quantity and attribute in cart
add_action( 'woocommerce_cart_calculate_fees','wc_cart_item_quantity_discount' );
function wc_cart_item_quantity_discount( $cart ) {
    if ( is_admin() && ! defined( 'DOING_AJAX' ) )
        return;

    // INITIALIZING VARIABLES
    $min_item_amount = 6; // Min quantity
    $discount = $items_count = $percent = $items_subtotal = 0;
    $taxonomy   = 'pa_variant'; // Taxonomy
    $term_slugs = array('flaske'); // Term/terms
    // Loop through cart items
    foreach( $cart->get_cart() as $cart_item_key => $cart_item ) {
      // Loop through variation
      foreach( $cart_item['variation'] as $attribute => $term_slug ) {
        // Only counting items that are above 6 and has attribute
        if( $cart_item['data']->get_price() >= $min_item_amount && $attribute === 'attribute_'.$taxonomy && in_array( $term_slug, $term_slugs ) ) {
            $items_count += $cart_item['quantity'];
            $items_subtotal += $cart_item['line_subtotal'];
        }
      }
    }
    // CONDITIONAL PERCENTAGE
    if ($items_count >= 6 ) {
        $percent = 15;
    }
    // DISCOUNT (TAXABLE)
    if( $items_count > 0 ) {
        // Calculation
        $discount -= ($items_subtotal / 100) * $percent;
        $cart->add_fee( __( "Mix & Match rabat - $percent%", "woocommerce" ), $discount, true);
    }
}

My current code works very well for variable products (the variants), but it doesn't seem to affect single products, even if I give the single products the same attributes as the variable product.

I suspect it has to do with the foreach loop foreach( $cart_item['variation'] as $attribute => $term_slug )

How can I make this work in general, so it also applies for single/simple products with same attribute flaske?

Any help and advice would be appreciated.

Other useful references:

Woocommerce percentage discount per item based on quantity

Exclude variations with 2 specific attribute terms from coupon usage in Woocommerce

You don't get the product attributes set in simple or variable products, in the same way as for product variations.

The following revisited code should also handle simple products (untested):

add_action( 'woocommerce_cart_calculate_fees','wc_cart_item_quantity_discount' );
function wc_cart_item_quantity_discount( $cart ) {
    if ( is_admin() && ! defined( 'DOING_AJAX' ) )
        return;

    // INITIALIZING VARIABLES
    $discount = $items_count = $percent = $items_subtotal = 0;
    $taxonomy   = 'pa_variant'; // Taxonomy
    $term_slugs = array('flaske'); // Term/terms
    // Loop through cart items
    foreach( $cart->get_cart() as $cart_item_key => $cart_item ) {
        $product = $cart_item['data'];

        // Product variations
        if( $product->is_type('variation') ) {
            // Loop through variation attributes
            foreach ($cart_item['variation'] as $attribute => $term_slug) {
                // Only counting items that are above 6 and has attribute
                if ($attribute === 'attribute_' . $taxonomy && in_array($term_slug, $term_slugs)) {
                    $items_count += $cart_item['quantity'];
                    $items_subtotal += $cart_item['line_subtotal'];
                }
            }
        } 
        // Simple products
        elseif ( $product->is_type('simple') ) {
            $attributes = $product->get_attributes();

            if( ! empty($attributes) && array_key_exists($taxonomy, $attributes) ) {
                $terms = (array) $attributes[$taxonomy]->get_terms(); // array of WP_Term objects
                $slugs = array_map(function($term) { return $term->slug; }, $terms); // Extract only the term slugs

                if (count( array_intersect($slugs, $term_slugs) ) > 0 ) {
                    $items_count += $cart_item['quantity'];
                    $items_subtotal += $cart_item['line_subtotal'];
                }
            }
        }
    }
    // CONDITIONAL PERCENTAGE
    if ($items_count >= 6) {
        $percent = 15;
    }
    // DISCOUNT (TAXABLE)
    if ($items_count > 0) {
        // Calculation
        $discount -= ($items_subtotal / 100) * $percent;
        $cart->add_fee(__("Mix & Match rabat - $percent%", "woocommerce"), $discount, true);
    }
}

It should work.