Unknown Gatsby Build Error -- while trying to enable incremental builds

It is, but it’s not as easy. There are 2 ways:

  1. Run a weird build command:

Something like

cd folder1 && npm run build && cd folder2 && npm run build && cp publish-dir-of-site-1 final && cp publish-dir-of-site-2 final

In other words, you need to cd to each of your site’s folder, build that, and copy that to a single directory that you can publish.

  1. Use Netlify Rewrites:

Simpler to implement, but can also lead to some issues depending on your setup. Just create 2 different sites, and use Netlify Rewrites to make them point to each other.

Here you go: [Support Guide] Making sure your builds use appropriate resources for Netlify's build system