How can I get post data or just post Id inside of a pattern?

I’ve created the following pattern file:

<?php
/**
 * Title: Post link
 * Slug: mytheme/post-link
 */
?>

<!-- wp:html -->

<div>
<?php 
    $id = $postId; //how can I get it????
    $post = get_post($postId);
    $slug = $post['slug'];
?>
<a href="<?= $slug; ?>">Some Button leading to a post</a>
</div>
<!-- /wp:html -->