As per the error details which you have shared with us we have figured out that It is an issue of the ionic setup, not code issue which we have used in our App.
But as per our search, we have found that the dependency of @angular-devkit/build-angular” is not installed at your system
Please run this command: npm install --save-dev @angular-devkit/build-angular to the root of your project
Or you can do rename node_modules and replace package.json with ours: https://we.tl/t-L7WsWiuCwo and run npm install . It will create a new node_modules(dependency folder). Then try to run ionic serve.