FormControl not patching values to multiple select

I'm working on a angular application but I ran into a problem I cant find the solution to. I'm trying to patch some preselected values to a form control (mat-select multiple) but it just wont show the values. It works fine with the control above (food), but when I try to bind to the multiple choice list, the values wont show.

//Here is my code:

  @Component({
  selector: 'app-add-edit',
  templateUrl: './add-edit.component.html',
  styleUrls: ['./add-edit.component.less']
})
export class AddEditComponent implements OnInit {
  pageTitle = '';

  order: Order;
  filteredUsers: User[] = [];
  id: number;
  orderToDisplay: Order = new Order();

  orderForm: FormGroup = new FormGroup({
    food: new FormControl('', [Validators.required]),
    usersOrdering: new FormControl('', [Validators.required])
  });

  constructor(private dialogRef: MatDialogRef<AddEditComponent>,
    private ordersService: OrdersService,
    @Inject(MAT_DIALOG_DATA) public data: any,
    private fb: FormBuilder) { }

  usersSelected: User[];

  ngOnInit(): void {
    this.id = this.data.orderId;

    if (this.id == 0) {
      this.pageTitle = 'Add a new order';
      this.order = new Order();

    } else {
      this.pageTitle = 'Edit the order';
      this.getOrder(this.id);
    }

    this.filterUsers(this.id);
  }

  save(): void {
    if (this.orderForm.valid) {
      if (this.orderForm.dirty) {
        this.usersSelected = this.orderForm.controls['usersOrdering'].value;

        if (this.id == 0) {
          this.order.food = this.orderForm.controls['food'].value;
          this.order.orderCount = this.usersSelected.length;
          this.order.restaurantId = this.data.restaurantId;
          this.order.usersOrdering = this.usersSelected;

          this.ordersService.addOrder(this.order)
            .subscribe(data => {
              this.dialogRef.close(true);
          });

        } else {
          this.order.id = this.id;
          this.order.food = this.orderForm.controls['food'].value;
          this.order.orderCount = this.usersSelected.length;
          this.order.usersOrdering = this.usersSelected;
          
          this.ordersService.updateOrder(this.order)            
            .subscribe(data => {
            this.dialogRef.close(true);
        });
        }
      }
    } else
      console.log('form is invalid')
  }

  dismiss(): void {
    this.dialogRef.close(false);
  }

  displayOrder(o: Order): void {
    if (this.orderForm) {
      this.orderForm.reset();
    }
    this.order = o;
    console.log(this.order.usersOrdering);
    this.orderForm.patchValue({
      food: this.order.food,
      usersOrdering: this.order.usersOrdering
    });
    this.orderForm.updateValueAndValidity();
  
  }

  filterUsers(orderId: number) {
    this.ordersService.filterUsers(orderId)
      .subscribe(data => {
        this.filteredUsers = data;
      });
  }

  getOrder(id: number) {
    this.ordersService.getOrder(id)
      .subscribe(data => {
        this.order = data;
        this.displayOrder(this.order);
    });
  }