Has anyone been able to successfully use the preview future to preview unpublished documents using the gatsby-source-prismic-graphql plugin?
Hey Madeline, thanks for reaching out.
Unfortunately, previews are no longer available when using the gatsby-source-prismic-plugin. We explain this topic in detail in this blog post.
What I can recommend you now is to first migrate to prismic-source-gatsby:
https://prismic.io/docs/technologies/migrate-to-the-recommended-plugin-gatsby
Then you'll be able to integrate your project with Gatsby Cloud, which will also allow you to run previews successfully!