To enable the Pre-order button, you can simply navigate to the Online store → Themes → Open theme editor → Navigate to Theme settings → Products → Preorder. From there, they can enable the pre-order button and customize it.
To hide the inventory text from your Product detail page and Collection pages for all PreOrder products. Just uncheck "Show inventory for pre-order products" and it will be removed.
Furthermore, you can add a delivery label to show messages or you can use metafields to display the content you want to show to your customers like estimated delivery time:
To access delivery label area, you will need to open the product page template > look for buy now button and click on it.
PS: Please know in order for a product to qualify as Pre-order it must be out of stock and Sell when out of Stock must be enabled in Shopify product editor.
