Here to me was because I forgot import a module.ts, and the console did not show about it. so, I only imported it and the angular worked ok. You can review all your modules.ts if there are some error with imports.

I faced similar problem with MatDatePicker. The problem was that I had imported MatDatepicker instead of importing MatDatepickerModule in the app.module.ts file.

So, check that you have imported MODULE not Component in your module file.

So I was just having a similar issue, and I was able to fix it by rearranging my import modules.

In my case, I was calling LoadingBarRouterModule before the main module LoadingBarModule. Check to see if you are loading the MatToolbarModule module before another required module and move it below that.

Maybe the selected answer could not be the correct one because you may want bundle the dependency when you are building the application.

From https://angular.io/guide/ivy#speeding-up-ngcc-compilation

In version 9, the server builder which is used for App shell and Angular Universal has the bundleDependencies option enabled by default. If you opt-out of bundling dependencies you will need to run the standalone Angular compatibility compiler (ngcc).

I'm opting of restarting the server everytime i'm adding a material component into AppModule. But if i'm wrong, please let me know.

For me it was due to unused (or rather broken) ValueAccessors – removing them fixed this.

What worked for me is importing the whole module for MatToolbar.

import {MatToolbarModule} from '@angular/material/toolbar'; 

And then adding MatToolbarModule to the imports[] array in my app.module.ts.

I imported some classes(FormControl, FormGroup, Validators) which are not modules in app.module.ts
I removed those classes and it solved my problem.

I found an error in imports section, i've added unexisting item.

import { MatMenuItem } from '@angular/material/menu';

and MatMenut item doesn't exist, i changed in MatMenuModule and after works

This used to happen to me whenever I imported 'MatToolbar' 'MatDialog' instead of 'MatToolbarModule' or 'MatDialogModule'.

stop your angular service (if you use command prompt or powershell ctrl + c) and run again(ng serve)

I solved it by removing the node_modules and reinstalled it.

Complete discussion here: https://github.com/angular/components/issues/18637

Add below specific configuration in package.json and npm install.

{
  "scripts": {
    "postinstall": "ngcc"
  }
}

Reference: https://angular.io/guide/ivy#speeding-up-ngcc-compilation

I had the same problem before, its because you modify your app.module.ts file while the server is running. Try to stop it and then run it again using the ng servecommand.