The SDN Neo4jDefaultCallbacksRegistrar and the reactive pendant will be a Noop in the upcoming 6.0.2 patch and deprecated. They will be removed in 6.1.
Comment From: snicoll
These are noop in 6.0.2, that's actually shipped in Spring Boot 2.4.1. I did reviewed that as part of switching our build to Spring Data's snapshot and we can remove these right away (https://github.com/spring-projects/spring-boot/issues/24284#issuecomment-740360516).