As for my case:

I want to manually assign 1 Action add product to cart, then create order and payment flow according to this order I create.

In this process the user only sees order information (like created with the default system) but they do not choose which products to add.

With current order system, the order is created when the customer actively chooses a product, puts it in the cart, and then at the checkout step, the system automatically creates an order for that product.