In reply to Anh Tran.

I find it's best to think of Gutenberg as one of many optional components of the edit screen. For posts and pages - anything with a generic "content" section - it usually makes sense to include a flexible block editor. For most custom post types that rely on custom fields, it doesn't. So when using register_post_type(), if you don't include the 'editor' in the 'supports' array, you don't have to deal with Gutenberg OR the classic editor and can rely entirely on custom fields (adding your own, more semantic wysiwyg fields if you like).