How do I add a Confirm Order button in Commerce Checkout?
I recommend starting at the website.com/admin/commerce/config/checkout/rules address, which will bring you to settings page where you are seeing "Express Checkout" options, which to my knowledge is not a PayPal feature and unfortunately is just shares the same name as their Express Payment Processor.

Next you want want to create a checkout rule, which will give you more control over the order process, which can be found at website.com/admin/commerce/config/checkout/rules

This process might start to get difficult, but essentially you want to create a Rule that will trigger a more detailed confirmation page, which can probably handled numerous ways and probably out of the scope of this question.