I checked with the team and the README for the Auth0 Angular SDK states that:
A library for integrating Auth0 into an Angular 9+ application.
Sorry about that. I’ll update the blog post to highlight the supported versions.
For Angular versions below 9, you can use the Auth0 SPA SDK:
Please let us know if you have any questions implementing Auth0 in your Angular apps using the Angular SPA SDK in a new topic here:
We do encourage customers to update to Angular 9 or higher when possible as the long term support (LTS) for Angular 7 has ended and LTS for Angular 8 ends in Nov 28, 2020.