This version of CLI is only compatible with Angular versions ^9.0.0-beta || >=9.0.0 <10.0.0, but Angular version 8.1.3 was found instead.

JavaScript
npm uninstall -g @angular/cli
npm cache clean
npm install -g @angular/[email protected] update @angular/cli @angular/core --allow-dirty --forceng update

Source

Also in JavaScript: