Can I show recommendations on checkout pages?
Unfortunately, Shopify apps cannot run on checkout pages and for that reason, the app widget won't show up on the checkout pages.
This is a Shopify intentional policy and no app can change that without breaking the Shopify 'terms and conditions' at https://help.shopify.com/en/api/app-store/listing-in-the-app-store/app-requirements#a-security
Please note that the situation is the same for all Shopify apps, not only Also Bought.
The app widget can be shown in product pages