S3 compatible storage is currently not supported with the S3 source and sink available as app starters for Spring Cloud Data Flow.
I added the S3 compatible storage support for new versions of the app starters using Spring Cloud Function available here with more information here.
Archive files built on Jul 8, 2020 (Commit #c397df1) are available here:
http://scdf-applications-jars.cfapps.io/s3-sink-rabbit-3.0.0-SNAPSHOT.jar
http://scdf-applications-jars.cfapps.io/s3-sink-kafka-3.0.0-SNAPSHOT.jar
http://scdf-applications-jars.cfapps.io/s3-source-rabbit-3.0.0-SNAPSHOT.jar
http://scdf-applications-jars.cfapps.io/s3-source-kafka-3.0.0-SNAPSHOT.jar