The run button is not clickable when the first job of the pipeline is parameterized.
A similar bug has already been opened and fixed a few years ago here, but I still have the same problem with the current version.
Please not that this new problem was also mentioned by Joel Njanga in a recent comment.
Related fix here, can't reproduce the issue described after this fix:
https://github.com/jenkinsci/build-pipeline-plugin/pull/78
Will be in 1.4.9 release. Can you build / deploy from master and see if this fixes your issue?
Attachment attached.