I’m not 100% sure, but from my experience setting up a shop, the checkout becomes hidden once PayPal is active, and you need to manually add the PayPal buttons to the cart.
So if you don’t add PayPal to the cart, by default there won’t be any buttons or payment methods for a user. When PayPal is connected, it doesn’t seem like you can let users go to the checkout page to complete their order-they must do it in this popup instead.
Which causes problems for me personally, as the default shipping address is always any other country than the one I’m retailing in-there is a script we can use to set the default for the checkout, but not this popup. So this has me stuck personally.