This is Elias with Shopify Support. I'd be happy to lend a hand with this!
The function for "Use the shipping address as the billing address by default" in the Checkout settings will be able to help customers skip writing their address again during checkout. However, if the shipping address page doesn't appear in the checkout, then it's possible that your products weren't marked as physical products.
When creating a product, there is a box that indicates whether this is a physical product or digital product. To disable shipping for digital products or services, we recommend leaving this box unchecked - This will signal the checkout to skip capturing the shipping address. However, since the shipping address page isn't appearing in checkout, then you'll need to make sure that all of your products and variants have this box checked.
If you need to check and mark multiple products, you can can use the bulk editor to edit up to 50 products per page. From the bulk editor, simply add the property for Requires shipping and make sure all of your physical products in that column is checked.
Once you've checked over your products and resolved the shipping page issue, you can re-enable the "Use the shipping address as the billing address by default" in your Checkout settings. That way, your customers can benefit from this feature and skip having to enter their address twice on your store.
Let me know if this was able to help you resolve the issue?