Here you will see all the domains applied to your headless environment.
You may choose to set them to PHP or NodeJS. Selecting either changes the fastcgi backend proxy in the Nginx configuration. If a domain is set to PHP, it will forward to PHP-FPM. (/srv/public_html/ or custom docroot) If NodeJS is selected, the requests will be routed to NodeJS. (/srv/pwa/)
This way you can host normal Magento 2 or PHP views alongside separate PWA applications for your store. Select and configure each domain as needed for your application.