As mentioned above the html field was removed from the GraphQL node. We know that some of you used this for e.g. gatsby-plugin-feed. Unfortunately, for compatibility and performance reasons we had to remove it. We recommend using the excerpt field in the meantime until we find a feasible solution to provide MDX rendered as HTML. If you have any suggestions, please comment on the GitHub Discussion.
After migration to MDX v2 in #712 html field is missing from RSS. This is due to breaking change https://www.gatsbyjs.com/plugins/gatsby-plugin-mdx/#v3-to-v4-breaking-changes