In PowerStore v3, you can add a product which does not belong to any category, which is why the category id column does not exists in the products table any more.
Instead, You might want to update the links to your product results page to include the category in the url, for example, you could have a link as follow:
Products_Results.php?Search=1&ProductCategoryID[]=1
or
Products_Results.php?Search=1&ProductCategoryID[]=2