Actually I'm evaluating different possibilites to better restructure our complex CD/CI pipeline.

One of the things I stumpled on was:

I'm able to start a defined job by it's known name

build job: 'knownJobname'

but I'm unable to create the job itself, if it doesn't already exist from the multibranch-pipline Job: desired

build job: 'knownJobname', from 'Jenkinsfile.job.knownJobname.groovy'

which should

1. checks for the given job
2. updates or creates the job
   1. perhaps should auto-update the name for multipipeline builds
3. run the build job with the given parameters

actually it just fails if the job doesn't exist: https://github.com/jenkinsci/pipeline-build-step-plugin/blob/4512e19/src/main/java/org/jenkinsci/plugins/workflow/support/steps/build/BuildTriggerStep.java#L100

In JenkinsDSL there was a pipelineJob which solved this:
https://jenkinsci.github.io/job-dsl-plugin/#path/pipelineJob
 

I'm quite unsure which of the "pluged in steps" is affected or should do/cover this.
The nearest hit is indeed https://plugins.jenkins.io/pipeline-build-step itself, but perhaps there should be a another "plugin" for it, or bundled in any "-support" / "-api" or "-cps-" plugin?!

P.S: should https://plugins.jenkins.io/workflow-job do the job?! I'm lost in documentations ;(
^ no, it's the Pipeline Job itself, not a step definition "plugin"