The various serverless platforms can be used with Spring Cloud Function by including an adapter jar in your classpath, and building the function artifact (JAR) in a way that works for the target platform. The project source code has explicit support for AWS Lambda, Azure Functions and Apache OpenWhisk. Some of the other platforms have their own support natively for Spring Cloud Functions (e.g. Riff and Oracle Fn).
The AWS adapter takes a Spring Cloud Function app and converts it to a form that can run in AWS Lambda.