Editing HTML Code for legacy posts/pages

Before Gutenberg, it was easy to click on the “view as html” button to edit the code of your post content. It made it possible to add divs and classes to specific paragraphs. It was an easy way to do with code what is now tackled with Gutenberg. Well, now I have a plethora of pages that have been converted to Gutenberg but still have the original code and a new theme to take advantage of Gutenberg and because old themes rely on old PHP.

Some pages end up looking like I can’t wordpress because I can’t access the html view of my posts’ content field to fix them.

Am I missing something? There needs to be a way for me to get in there and look at the code of my post content. How do I do this now?