That’s a very good point that I had not considered. Thanks @Ian_W
The Jenkins platform SIG stopped testing Jenkins on the Eclipse OpenJ9 / IBM Semeru Java virtual machine two years ago (or more). However, IBM Semeru is the only reasonable choice if you need to run Java 8 on an IBM s390x mainframe because the Hotspot virtual machine is not available for IBM s390x. It worked well for me when I needed Java 8 on s390x.
Later versions of the Eclipse Open9 / IBM Semeru JDK have been reported to have issues when running Jenkins. No one is investigating those issues or putting effort into fixing those issues. Refer to Failed to start Jenkins Continuous Integration Server for a report from one user. The Jenkins issue tracker records others issues with OpenJ9 / Semeru.
If someone wants to investigate and resolve Jenkins issues with OpenJ9 / Semeru, they are welcome to join the platform SIG where we discuss those types of topics.