John,
No, it is not in scope for the exam.
The OCP 8 exam did have the fork/join framework in scope with the objective:
Use parallel Fork/Join Framework
Unsurprisingly, we covered it in our 809 (OCP 8) book. The topic is not in scope for the
Java 11 exam which is why you don't see it covered in the 819 (OCP 11) exam.