In order to get a temporary fix...
- Switch your update center to the Java 11 experimental update center https://updates.jenkins.io/temporary-experimental-java11
- Install the Pipeline: Support plugin v. 3.0-java11-alpha-1
Note that the release is not fully compatible with the 2.x version. You should ensure that there is no running Pipelines at the time of the upgrade. A final solution is currently in progress in JENKINS-51998