High-Performance Order Storage HPOS) also previously known as “Custom Order Tables” is an opt-in solution that provides an easy-to-understand and solid database structure – specifically designed for eCommerce needs. If enabled, it provides an alterate method for storing WooCommerce data instead of using wp_posts and wp_postmeta tables. This will not be moved into WooCommerce Core until next year. If you enable the Formidable WooCommerce add-on, which is not compatible with HPOS, then the HPOS option will be disabled. If you need HPOS enabled, I suggest you open a ticket with Strategy 11 to request a feature update.