To fix missing disk performance counter in Task Manager:
1 Use Win + X key combination to open menu, click on Windows PowerShell (Admin) to open elevated PowerShell window.
2 Close Task Manager if you have it open
3 Type following command and hit
4 Now open Windows Task Manager again, the disk performance counter should appear.
Note: To diesable it again, just repeat these steps but replace diskperf -y with diskperf -n