WP Basic Issue

Gutenberg was built into WordPress 5.0 as the Block Editor, that was a few years ago: https://ww.wp.xz.cn/documentation/article/wordpress-block-editor/

So, to get the Block Editor for use on posts/pages, just update to the latest version of WordPress.

If you’re referring to the Site Editor, which lets you customize the whole site, that was a bit more recent: https://ww.wp.xz.cn/documentation/article/site-editor/

To have the Site Editor, update to the latest version of WordPress, but you will need a Block Theme to make use of it: https://ww.wp.xz.cn/themes/tags/full-site-editing/