How to Invoke Apex from Flows Using InvocableMethod Annotation | Salesforce Developer Support

InvocableMethod annotation is used to identify a method in Apex class that can be called from a flow, a Bot, or an NBA Strategy. It is a helpful method to provide a seamless admin-friendly way to call the Apex code using simple flows. Invoking Apex from flow is a significant option for providing design patterns that can solve many business problems while also providing great user experience.
Knowledge Article: Developer documentation on the @InvocableVariable annotation -