placeholder in angular 9 select with working required

1Set initial value of month = null in the component.ts and
2add [(ngModel)]="month" in the select tag of component.html.
3
4//component.ts
5month = null;
6
7//component.html
8<form  #filter="ngForm" (ngSubmit)="filterta(filter)" style="display: flex;">
9       <select name="month" [(ngModel)]="month" #month required>
10                <option [ngValue]="null" [disabled]="true" >All</option>
11                <option value="1">January</option>
12       </select>
13</form>

1<form role="form" class="form form-horizontal" (ngSubmit)="onSubmit()" #form="ngForm" ngNativeValidate>
2    <div class="form-group row">
3        <div class="col-xl-4 col-lg-6 col-md-12">
4            <fieldset class="form-group">
5                <label for="customSelect">Categories:</label>
6                <select class="custom-select d-block w-100" id="Category" [(ngModel)]="Category" name="Category" required placeholder="d.ff">
7                    <option hidden [value]=""  selected>Select one category </option>
8                    <option *ngFor="let item of myBusinessList" [value]="item.id">{{item.name}}</option>
9                </select>
10            </fieldset>
11        </div>
12    </div>
13    <button type="submit" class="btn btn-raised btn-danger">Save</button>
14</form>
15

1[value]="" selected hidden
2//add hidden with selected