Specific Products tasks have no rule a new product could match, so the option is disabled.
When you choose Specific Products on Let's Get Started, the auto-processing checkbox is disabled and Describer shows: Auto-processing new products is not available when selecting specific products. Choose "All Products" or "Specific Collections" to enable this feature.
Why
A Specific Products task is a fixed list. A product you create tomorrow cannot be part of that list, so there is nothing to match it against.
What to do instead
- For all future products: create a task on All the Products with auto-processing on
- For one category: create a task on Specific Collections, and make sure new products are added to that collection, for example through an automated collection