According to the documentation you can pass an array to exclude the field names like: Besides, excludedRoutes is a configuration only allowed in gatsby source-wordpress, not in the experimental version.
It always depends on your filesystem and how it is set up. The short answer is that allFile retrieves all kind of files (images, markdowns, JSONs, etc) set in your gatsby-source-filesystem while allMarkdownRemark only fetches the markdown files because a transformer plugin has previously created a specific node to do so. allMarkdownRemark, of course, is more specific and has better performance, … Read more