Trouble getting started with Gatsby on codesandbox, runkit - reactjs

Question

I wrote a React component that I want to demonstrate with examples. The component is visible here: https://codesandbox.io/s/live-retractable-toc-for-documentation-g4zv99 . In short, the component takes the content of the HTML output and generates a dynamic local table of contents from the h1-h5 headers. It dynamically adjusts to which headers are visible as the user scrolls, disappears when it might conflict with wide tables or images (for more info, see FAQ in README.md).
A Gatsby-based example seems a reasonable choice to show the component in action. But I have a problem with getting Gatsby to work on codesandbox. The newest version of nodejs offered in the list of dependencies is 16, while the latest Gatsby requires 18. I have tried to adjust package.json to work with the available versions, as follows:
{
"name": "gatsby-minitoc",
"private": true,
"description": "",
"version": "0.1.0",
"author": "Francis Vila <fvila789#gmail.com>",
"bugs": {
"url": "https://github.com/gatsbyjs/gatsby/issues"
},
"dependencies": {
"#fontsource/merriweather": "^4.5.14",
"#fontsource/montserrat": "^4.5.13",
"gatsby": "4.25.3",
"prismjs": "^1.29.0",
"react": "^16.9",
"react-dom": "^16.9"
},
"devDependencies": {
"prettier": "^2.8.1"
},
"homepage": "https://github.com/gatsbyjs/gatsby-starter-blog#readme",
"keywords": [],
"license": "0BSD",
"repository": {
"type": "git",
"url": "git+https://github.com/gatsbyjs/gatsby-starter-blog.git"
},
"engines": {
"node": ">=14.15.0"
},
"scripts": {
"build": "gatsby build",
"develop": "gatsby develop",
"format": "prettier --write \"**/*.{js,jsx,ts,tsx,json,md}\"",
"start": "gatsby develop",
"serve": "gatsby serve",
"clean": "gatsby clean",
"test": "echo \"Write tests! -> https://gatsby.dev/unit-testing\" && exit 1"
}
}
(visible here: https://codesandbox.io/s/gatsby-minitoc-v15mu9?file=/package.json:0-1058 )
But I get an error as follows:
error Command failed with exit code 1.
info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.
The linked page does not tell me what's wrong or how to fix it...
I tried to use runkit (see here https://runkit.com/francisvila/63c52b50791d8600082b3933 ) but got a cryptic message when trying to add Gatsby dependency
Error: Cannot find module 'react'
Should we have react?
We should have every package on npm. Sometimes this error is caused by a typo in your require path, but if you think we are actually missing this package, please confirm below and we’ll do our best to fix it as soon as possible!