Download mapswitcher.zip, extract, and drop the mapswitcher folder into client\your-extensions\widgets so manifest.json sits directly inside it. Then install dependencies in the client folder (npm install on Experience Builder 1.20 and earlier; pnpm install on 1.21 and later) and restart the client. Visual Studio type shims (src/*.d.ts editor files) are left out of this zip on purpose; they are in the GitHub repo if you want them.