In PreOrder Now, the app works by replacing the existing Add to Cart button with a Pre-Order button when the product matches your preorder settings.
Because of this, the app does not support showing both buttons at the same time on the same product page.
How PreOrder Now Works
When a product or variant is enabled for preorder:
The normal Add to Cart button is converted into a Pre-Order button
Customers use that single button to place the preorder
The original Add to Cart button is not shown separately
This behavior is expected and is how the app is designed to function.
Can I Create a Separate Pre-Order Button?
At this time, PreOrder Now does not include a built-in feature to display a second standalone preorder button alongside the normal Add to Cart button.