Upsell & Addon Sections | Auto-Checked Toggled by Default

It's not as straightforward as it may appear.

Ensuring the checkbox is selected by default upon page load is the easy aspect of the ask.

However, doing so entails that when a customer adds an item to the cart, this additional item should be automatically included — taking into account validations such as inventory, variant options, and the add-to-cart functionality.

Consequently, this "prechecked" functionality should inherently add the extra addon item upon the page load (in the backend) to enhance user intuitiveness.

As it is currently designed, the system waits for the toggle action to be triggered. This is the most basic and secure approach applicable to nearly every theme (given that each theme manages the cart uniquely).

Nevertheless, displaying the preselected state upon loading should also trigger the addition of the upsell item.