I want render my size array in dropdown my array look like this at the moment

[tidal reef]

[
    {
        "id": 4,
        "value": "Black",
        "sell_price": 1000,
        "cost_price": 400,
        "size": [
            {
                "id": 5,
                "value": "S"
            }
        ],
        "attachments": [
            {
                "id": 2,
                "product_attachment_details_attachments": {
                    "": 15
                }
            }
        ]
    },
    {
        "id": 4,
        "value": "Black",
        "sell_price": 1000,
        "cost_price": 400,
        "size": [
            {
                "id": 6,
                "value": "M"
            }
        ],
        "attachments": [
            {
                "id": 2,
                "product_attachment_details_attachments": {
                    "": 15
                }
            }
        ]
    }
]

i try this render this in this way but it showin error

<select [(ngModel)]="selectedSize">
 
  <option *ngFor="let product of filteredProducts ; let i=index" *ngFor="let size of product.size"
    [ngValue]="size.value">
    {{size.value}}</option>
</select>

[red tree]

You cannot use two structural directive on the same element.
And in the specific case, it makes little sense to iterate two times on an element.

You probably want two separate select bound to each other.
The first one letting the user select a product, and the second one letting him select a size for the selected product.