Drupal's front end can be decoupled by creating a headless application. Drupal uses JSON API as a flexible way to retrieve content to display. You can also create custom REST endpoints that support the app's requirements.
Whether the app resembles the Drupal site, or will be entirely different is a big distinction. A Drupal site's pages are made up of content, views, forms, and custom controllers. These all have to be accounted for in the app, along with the routing. When a visitor goes to a URL, the app checks Drupal for the page and gets JSON output to render the response. This works great for content, but other things that Drupal renders will take more effort to rebuild, especially for forms.
Modules