We have successfully upgraded the Jenkins controller to Java 21. Additionally, we updated the agents from Debian 12 to 13 to fully support the new Java runtime. Post-upgrade, we encountered some issues with the packaging pipelines due to new ruby version dependencies(Debian13 includes ruby 3.1 ), However, @evgeni has since resolved these.
[1]: Switch Jenkins to Java-21 by devendra104 · Pull Request #2398 · theforeman/foreman-infra · GitHub