example app can't be built

The example app has a mix of angular 7 and angular 12 dependencies which conflict with each other.
Also uses @ionic/angular 4.x, which is not compatible with angular 12

It's not possible to install on npm 7+ because of peer dependencies.
If you install with `npm install --force` or use npm 6, it installs, but then `npm run build` fails with multiple errors.

Start in the example app's dependency configuration and compare the Angular and @ionic/angular versions. Run npm install with npm 7 or newer, then npm run build to reproduce the reported failures. Done means the dependencies install without force and the example app builds successfully.

Written by the indexing model from the issue text.