To add the Instant PDP button anywhere, copy and paste this block into a .phtml

            <?php
                $instantCheckoutHtml = $this->getLayout()
                ->createBlock('Instant\Checkout\Block\PdpBlock')
                ->setProduct($product)
                ->setTemplate('Instant_Checkout::ic-pdp-btn.phtml')
                ->toHtml();
                echo $instantCheckoutHtml;
            ?>