In Product single settings, you can config Pick mode, Hide sold-out variants
1. How to access the Product Single?
Step 01: From Shopify Admin, click on Online Store > Select Themes > In the Current theme section, click the Customize button.

Step 02: In Theme settings (Customize) > scroll through the list to find and open the Product Single tab.

2. How to configure the Product Single?
Pick mode: Allows users to quickly select product options and variants.
Hide sold out variants: Automatically hides variants that are out of stock. Not applicable for product sold out.