Hi,
This is unfortunately not possible without using the index table engine + using a custom code to index non whitespaced SKUs.
1. Add this custom code to the functions.php in your theme/child theme directory (copy from line 3 only!). Before editing, please make sure to have a full site back-up just in case!
2. Make sure to configure and enable the index table engine:
– Creating the index table
– Enabling the index table
Don’t forget to choose the product custom post type, as well as the _sku custom field for indexing.
After generating and enabling the index table, the SKUs without the whitespace will be indexed as part of the content.