The Javadoc packaging tools that combine the generated Javadoc for Jenkins weekly releases, Jenkins plugin releases, and Jenkins component releases are currently using Java 8 to run their Groovy code that combines the many different Javadoc archives into the final site https://javadoc.jenkins.io

We should use Java 11 in those packaging scripts to further reduce dependencies on Java 8.

See the community.jenkins.io recommendation from notmyfault for more details.