If 'mat-label' is an Angular component, then verify that it is part of this module. code example
Example: 'mat-label' is not a known element:
// common-widgets.module.ts
import { MatFormFieldModule } from '@angular/material/form-field';
import { MatInputModule } from '@angular/material/input';
@NgModule({
imports: [
MatFormFieldModule,
MatInputModule
]
})
export class CommonWidgetsModule { }