WordPress comes with a large library of embed blocks to embed content from other sites such as YouTube, Spotify, Reddit, etc.
They are all inserted on this page for testing, but none of the blocks have embed URLs actually entered. If no URL is entered (or if the URL has an error), nothing will render on the front end. Unless you are viewing this page in edit mode, it will look blank.
If you plan to use an embed in your site, you can use this page to test it.