Quick Buy Button can be enabled In Single Product Template Button block which is variation of Add to cart Button block but it’s made for Single product pages
It looks next
The difference between the regular Add to Cart and Buy Now buttons is that the latest one redirects the user directly to the checkout page after a click. While the regular button adds a product to the cart, the user must visit the cart page, then go to the Checkout page.
Each of these steps can reduce conversion on-site because the user can change his mind.
Also, there is option to disable regular Add to cart button so your site will have only Quick Buy button on single pages