There are plenty of questions and tutorials on this topic, but none of them cover all use cases for a chrome extension, because most of them assume there's only one entry point.
Here are the requisites:
Multiple "single page applications":
1) popup.html for the extension pop up page
2) options.html for the options page
3) custom.html this is a custom .html file that the extension can refer to "locally"
Each of these files are entry points for React to manipulate the DOM, but they behave independently of each other.
Non React TypeScript files
They must not be bundled together with any other scripts, and gets compiled to its own JavaScript file, for example a background.ts that compiles to background.js (which is refered to in the manifest.json).
I assume this is doable with TypeScript, React and Webpack but I'm not sure how to approach that.
I found a solution but it was not using create-react-app and webpack. It looks like parcel supports multiple entry points out of the box without any configuration.
Assuming a directory structure like this:
├── chrome
│ └── background.ts
├── html
│ ├── custom.html
│ ├── options.html
│ └── popup.html
├── manifest.json
├── package.json
├── react
│ ├── custom.tsx
│ ├── options.tsx
│ └── popup.tsx
With Parcel.js you simply do:
parcel build html/*.html react/*.tsx chrome/*.ts
And it will handle the multiple entry points. I created a repository that contains a template for that approach, it contains a fully runnable example.