In the Classic editor, if you're in Text mode and you click on the Add Media button, the media modal pops up. You can then select an image, and its raw markup will be inserted into the post content. You get the same markup as you would performing that operation in Visual mode.

In Gutenberg, however, if you switch to the Code Editor and add an Image block, you just get placeholder markup:

<!-- wp:image -->
<figure class="wp-block-image"><img alt=""/></figure>
<!-- /wp:image -->

If you select a table block, all you get is <!-- wp:table /-->

Reported on the forums.

I'd expect the block GUI to pop up and allow selection of options, etc. Then, the proper markup should be inserted into the post content.