Schema Builder

Removing all posts or querying ACF flexible content that isn't set on one post will usually break a Gatsby site's build. Schema builder is a post type where you can fill all the fields you want to be part of your schema wether they exist yet or not. This post type is filtered out and pages aren't created for it. If you query for all post types at once, you'll need to filter it out yourself.

You can build your schema from the WP backend by going to Development->Schema Builder.

Create a post and add dummy data to all fields that you don't want to break if they're empty.