Symfony UX makes Symfony a Full Stack Framework (again)
Symfony UX provides developers comfortable with backend domain with PHP and Symfony to interactivity to the front end with preferred tooling and documented conventions. With server generated core markup, you could call it back end driven front end development. This will certainly not be something for everyone, but it need not be. You are free to use Symfony as your backend for a pure API or use Webpack Encore to build a full stack app in a monorepo with React.js client app for example.