While creating Trusted App, user can select from the wide array of available API Products. These API Products are driven by entitlements.
Each API Product is published to specific application group during the onboarding process. If you are unable to see API Products, then you might be missing your application specific group association.
What is the difference between an API and an API Product?
API stands for Application Programming Interface, which is a software intermediary that allows two applications to talk to each other. An API product bundles resources [such as API proxies] in order to provide a specific level of access and functionality for client app developers. On the other hand an API product typically specifies a list of API proxies, along with access limits, API key approval method, and other configuration that should be in place for all of the bundled proxies.