No, the alternative product will not appear automatically after enabling the feature globally. While the plugin provides a global toggle to Enable Alternative Products, you need to manually assign the alternative product(s) for each discontinued item at the individual product level.
After enabling the feature from the global settings, go to the edit screen of a specific product that you want to mark as discontinued. There, you will find a field to select alternative products. Once saved, these alternatives will appear on the product page along with a styled notice, based on your global style settings.
This manual selection ensures you have full control over which products are suggested as alternatives, maintaining relevance and quality of recommendations for your customers.