I've looked all over for this answer but cannot find it, as most of the answers are how to add JDK to Jenkins for usage within a test. I'm looking for how to ensure Jenkins itself is using OpenJDK 11 that I have installed and not the older JDK 8.
I have checked the Jenkins.xml and it does point to OpenJDK 11 as well as the %java_home% and PATH in the system environment are pointed to the correct locations.
When I check System Properties, I still see things related to Java 8 (java.home, java.specification.version, etc.)
I have no idea where else it could be stored at to change this.
In your Jenkins UI select Manage Jenkins → Status Information → System Information (displayed as System Properties then; in Jenkins 2.289.3, at least) → search for java.runtime.version or others to look for hints what's possibly going wrong.