I was hoping v 22.0 would change this, but I am still having the same problem…
In menu 2.2: Select data to search in, if Product type is selected, custom product attributes are not listed individually but rather just _product_attributes serialized field if they are not archive types (are not taxonomies, but just single field values).
So if I want to make a slider for example for _pa_year_published which is a custom attribute, but not taxonomy, how can I get WPSOLR do index this data?
Custom attributes are not specifically supported (by opposition to global attributes, which are taxonomies).
But if they are stored as custom fields, they should be indexable.