As I continue to fiddle with GatsbyJS, one thing I noticed is that you cannot specify the output directory of the GatsbyJS build. This was requested, implemented, and then reverted in GatsbyJS. In fact, it may never become a feature.
As I have begun working with GatsbyJS once again, I am trying to find a way to work with GatsbyJS and Drupal locally in a somewhat streamlined fashion. Honestly, serving Drupal over PHP's built-in server and using the gatsby develop and gatsby serve command work just fine. But, I love tooling.
I have been tracking down an interesting quirk when parsing JSON:API resources with the Drupal source plugin for GatsbyJS. I have a test environment with the JSON:API Schema module installed and was receiving errors about data in the links property.
The Drupal community has taken to GatsbyJS, the React framework that lets you easily build static (and more) websites (or applications.) And, honestly, this makes a lot of sense. Drupal is a great content management system and it even has ways to create microsites within one installation (thanks to techniques like the Domain module.)