When the new PDF2XL product line was released in 2019, many changes were applied to the different editions. One of those changes was the xRay (Advanced) OCR capability added to the Enterprise plan.
As an Enterprise feature, this option is disabled in all other plans and the perpetual PDF2XL Pro license.
This is a secondary OCR engine that you can enable in your Enterprise application if you find the default OCR engine is not working well enough. It allows you to use all the OCR Tweaking settings available in the Options and has more languages to choose from.
If you have the Enterprise plan, and your Advanced OCR is disabled, it's likely that your machine is not compatible with the requirements of that OCR engine.
To run Advanced OCR, you require AVX2 support, available in most processors released since 2012.
If you don't know this information, locate the CPU model number from your system information and look it up on the manufacturer's website.