It's because a lot of the imports has been changed since NativeScript 8, not just Angular related modules.
You can solve it by replacing the imports that you have in your code with:
import { NativeScriptFormsModule } from '@nativescript/angular';
Or
- Just delete it, then reimport it by deleting and rewriting the last character of the class name, or just use the shortcuts defined on your IDE.
- if you are installing the needed module, you will get a suggestion just where you used that class.
this is a silly solution, but I use it all the time, it's going to save you a lot of time, so you don't have to look at the right imports on the internet.