If 'mat-option' is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of this component to suppress this message. code example

Example 1: add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of this component to suppress this message

//In the app.module.ts
import { NgModule, CUSTOM_ELEMENTS_SCHEMA } from '@angular/core';
...
@NgModule({
  declarations: [ ... ],
  exports: [ ... ],
  imports: [ ... ],
  schemas: [ CUSTOM_ELEMENTS_SCHEMA ]
})

Example 2: 2. If 'app-navbar' is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of this component to suppress this message.

import { NgModule, CUSTOM_ELEMENTS_SCHEMA } from '@angular/core';