NPM Workspaces is a powerful way to manage a suite of javascript / typescript applications in a monorepo.
NPM Workspaces was introduced with version 7, so if you are using an earlier version anywhere in the build flow, the build will fail.
npm run start -w @rnw/todo
Create React App doesn't compile outside of its src directory, so react-app-rewired is needed with customize-cra to allow for directories outside of the CRA app to be transpiled.