Google is testing adding a "loyalty benefits" section to the merchant/retailer knowledge panels. This would show on the right side of the page, under the description of the retailer.
Brodie Clark spotted this and wrote on X, "Google is now testing out a new section for loyalty program benefits attached to merchant knowledge panels. It shows quite prominently on both mobile and desktop, with costs labelled clearly."
Brodie also posted a heck of a lot more detail on his blog here.
Here is his screenshot of this feature:
In 2022, we saw Google list loyality programs when you click on a specific store. Here is what that looked like:
Loyalty program details can be entered in Merchant Center.
Forum discussion at X.