I just got same error. If you are using Angular 9 in your app check version of @angular-devkit/build-angular. I had version 0.1000.0 which I assume is intended for Angular v10. Probably got there by running ncu I just downgraded on 0.9xxx.x and this error message is not showing anymore.
To fix this issue just downgrade angular-devkit/build-angular:
npm install @angular-devkit/build-angular@0.901.9