You can automatically hide sold-out products in a collection by using Shopify’s built-in collection rules. No additional apps are required.
This method works when the collection type is Smart.
Go to Shopify Admin → Products → Collections.
Create a new collection or edit an existing one.
In Collection type, select Smart.
Add the rule:
Inventory stock → is greater than → 0
Save the collection.
After this rule is applied, any product that becomes sold out (inventory = 0) will automatically be removed from that collection. When the product is restocked, it will appear in the collection again automatically.

This works only with Smart collections.
If you are using a Manual collection, you will need to remove sold-out products manually or use an app to automate this behavior.