In WooCommerce, products cannot be filtered by custom (product-level) attributes. These attributes exist only within individual products and are not indexed for filtering in the catalog.
To enable filtering (for example, using layered navigation or filter widgets), you need to convert your custom attributes into global attributes. Global attributes are stored as taxonomies, which makes them usable for filtering the spreadsheet.
Good news: we have a step-by-step tutorial that shows you exactly how to convert custom attributes into global attributes.
Convert custom attributes to global attributes (and vice versa)
Once your attributes are global, you’ll be able to use them as search filters in the spreadsheet.