that's interesting, certainly /usr/share/elasticsearch/jdk/bin/java -version returns:
openjdk version "14.0.1" 2020-04-14
OpenJDK Runtime Environment AdoptOpenJDK (build 14.0.1+7)
OpenJDK 64-Bit Server VM AdoptOpenJDK (build 14.0.1+7, mixed mode, sharing)
which is not the java-1.8.0-openjdk-headless-1.8.0.252.b09-3.el8_2.x86_64 i installed, and uninstalling openjdk does not try to uninstall any of ELK as a dependency, and ps auxw|grep java shows the ES version running, so seems like openjdk is not required, but would like confirmation.