Why is Angular form not validating?

Question

Angular

Hello, I created a form, it has a DatePicker, I use https://materializecss.com/pickers.html, the form works successfully, opens and selects the date and also inserts it into the input, but the problem is that Angular does not see the changes and thinks Input is still empty and asks for a date. But if you use the standard DatePicker from input type="date", then everything works.

<div class="input-field">
      <input
        type="text"
        id="preparationStartDate"
        formControlName="preparationStartDate"
        #preparationStartDate
        [ngClass]="{'invalid': form.get('preparationStartDate').invalid && form.get('preparationStartDate').touched}"
      >
      <label for="preparationStartDate">Начало</label>
    </div>

ngOnInit() {

    this.form = new FormGroup({
      preparationStartDate: new FormControl('', Validators.required)
    })
}

ngAfterViewInit() {
    this.preparationStartDate = MaterialService.initDatePicker(this.startRef, null)
  }

I'm new to Angular, can you please tell me how to fix the error so that after selecting a date through materialize datepicker, the form becomes valid?