the added quantity is always 1 regardless of the entered value
there is a bug in the file "ProductAttributeParser.cs" line 920
it should be:
if (formKey.Equals($"addtocart_{product.Id}.AddToCart.EnteredQuantity", StringComparison.InvariantCultureIgnoreCase))
instead of
if (formKey.Equals($"addtocart_{product.Id}.EnteredQuantity", StringComparison.InvariantCultureIgnoreCase))