Imagine a PHP backend providing an API for an app. The only HTML ever produced will be the admin backend, and perhaps auth forms for special cases. The surface of the API will produce objects serialized to JSON, and the vast majority of the PHP will be business logic to talk to external services and do what the service is paid for.

Some might not like the language, but whole businesses will run on PHP, with a dedicated react or next.js frontend that only talks to the PHP via API.