When you only want to include a small part of your products to your product feed and they do not have a common denominator on which you can create an “include only” filter you need to solve this differently. The easiest way to do so is by using the WooCommerce product tags.
Step 1: create a product tag
Go to “Products > Tags” and create a tag like this:
Step 2: assign the product tag to your products
On your product edit pages you add the tag you just created. You need to do so just for the products you want to be part of your product feed.
Step 3: create the include only filter
When you are done adding the product tags to your products you can create an include only filter on the created tag like this:
And that’s all. Only the products that contain the above product tag will make it to your product feed.