I took five Red Hat Exams within the last six months and have to say, the by far hardest one was EX442 (Certified Specialist in Performance Tuning). Despite a lot of experience with Linux Systems and intensive preparation, I wasn't able to pass the Exam.
The areas "Using utilities to monitor system and application behavior" and "Configuring PCP monitoring" were most challenging and caused me to fail.
I used the A Cloud Guru Course to prepare, which I didn't found much helpful to be honest. Experience was quite similar is during my preparation for the "Red Hat Certified Specialist in Linux Diagnostics and Troubleshooting", mainly high level, lot of Exam relevant stuff missing and so on.
I still had the eBook from my expired Red Hat Learning Subscription available, which I used in addition after finishing the ACG Course. But this time, even this wasn't enough.
During the Exam, tools and techniques are required which were even in the offical Course documents more or less just a side node on a Page, not marked as somehow important or part of any Lab.
Heard rumors that Red Hat internal this Exam is called "the widow maker" and known to be very hard. Might also related to the fact that the Topic is quite specially and sometimes a little boring ;)
So overal I just picked the wrong Exam, I learned a lot so it wasn't wasted time, but for the three other Exams required to become a Red Hat Certified Architect, I will probably focus more on Kubernetes / OpenShift, let's see.