I want to be able to filter products by Product category in Inventory Valuation

So what I do is add a field to the search view:

<field name="product_id" string="Product Category" filter_domain="[('product_id.categ_id', 'child_of', self)]" />

it works but it doesn't do exact matching of ID (which shows result in a dropdown as you type)

I see \here that the operator="child_of" can solve this but how can I use it on a product_id.categ_id in my case?