The official VCP65-DCV Exam Preparation Guide covers a lot of security topics, but the vSphere 6.5 Troubleshooting guide is definitely more rich, with more content.
For example, there are several missing parts, such as some possible examples of wrong VMs configuration, not related to the allocated resources, but related to specific VMware functions (for example, device passthrough).
Also, some common issues are totally ignored, like the way you recover Orphaned Virtual Machines (https://docs.vmware.com/en/VMware-vSphere/6.5/com.vmware.vsphere.troubleshooting.doc/GUID-BFD8C9BC-30FB-4A92-AFEC-2FC9FF387920.html).
The VMware vSphere: Troubleshooting Workshop course is recommended so that you can learn more about these specific tasks.
For the VCP-DCV exam, you just need basic knowledge. Deeper knowledge will be useful for the VCAP exams that are related to the DCV path...