Which statement about the @InvocableMethod annotation is correct?

The statement regarding the @InvocableMethod annotation being able to allow methods to be called from Flows, Processes, and REST APIs is accurate. This annotation is designed specifically for enabling method invocation from various Salesforce automation tools, including Flows and Process Builder, as well as accessing these methods through REST API calls.

By using the @InvocableMethod annotation, developers can create flexible Apex methods that can be executed in different contexts, making it easier to integrate custom logic within the declarative features of Salesforce. This functionality allows for greater reusability and provides an intuitive way to invoke Apex code without needing to write specific API calls or have extensive custom logic stitched into the flow or process definitions.

The other options do not correctly capture the essence of the @InvocableMethod annotation. While it may lead to reduced code complexity, this is not its primary purpose. Additionally, the context of synchronous or asynchronous flows doesn't restrict its use, nor does it require a companion framework to function.