вы можете достичь своих требований, как это,
вот пример,
в app.component.html
<mat-form-field>
<mat-select placeholder="Toppings">
<mat-option *ngFor="let topping of toppingList; let i =index" [value]="topping">
<mat-checkbox [checked]="selected === i" (change)="onChange(topping);selected = i"> {{topping}}</mat-checkbox>
</mat-option>
</mat-select>
</mat-form-field>
и app.component.ts
export class AppComponent {
toppingList: string[] = ['Extra cheese', 'Mushroom', 'Onion', 'Pepperoni', 'Sausage'];
selected = -1;
/*checkbox change event*/
onChange(event) {
console.log(event)
}
}
вот Stackblitz демо