CODE EXAMPLE FOR JAVASCRIPT

angular mat select open programmatically

<mat-form-field appearance="fill" class="myfilter">
  <mat-label>Toppings</mat-label>
  <mat-select multiple #filter>
    <mat-option *ngFor="let topping of toppingList" [value]="topping">{{topping}}</mat-option>
  </mat-select>
</mat-form-field>
<button mat-raised-button color="primary" (click)="filter.open()">check</button>