When using springboot with elasticsearch, you need to be explicit with some transitive dependencies as SpringBoot declares a version 6.4...
Basically you can put this in your pom.xml:
<properties>
<elasticsearch.version>7.7.0<elasticsearch.version>
</properties>
See documentation here: https://docs.spring.io/spring-boot/docs/current/reference/html/howto.html#howto-customize-dependency-versions
What is the output of
mvn dependency:tree