custom mat-autocomplete iconm
<mat-form-field class="col-12">
<mat-label>{{label}}</mat-label>
<input type="text" matInput [matAutocomplete]="auto">
<i class="material-icons align-arrow-right">arrow_drop_down</i>
<mat-autocomplete #auto="matAutocomplete" dropdown-arrow="true">
<mat-option *ngFor="let option of options" [value]="option">
{{option}}
</mat-option>
</mat-autocomplete>
<mat-hint>{{hint}}</mat-hint>
</mat-form-field>
...
.align-arrow-right {
position: absolute;
right: 0; //change as per requirement
top: 0; //change as per requirement
}