Shopify by default does not hide out-of-stock products from neither your main store catalogue nor your collections. Hiding out-of-stock products is a very reasonable request for any store and will require some tinkering with your store’s settings.

Shopify provides official documentation on how to achieve this:

• Hide out-of-stock products from your collections
• Hide out-of-stock products in your default Catalog collection

You can read the full guide here.