Hi Marty,
I am Sumit here to assist you with this question.
Microsoft removed it because it was never an accurate tool - as usage depends on the load on the resources. Microsoft is tracking feedback for it, though.
You may be able to downgrade to Windows 10 if it is a new PC. I would suggest asking manufacturer for the same. If you upgraded manually, do a reinstall.
How to do a clean install
https://answers.microsoft.com/en-us/insider/for...
https://answers.microsoft.com/en-us/windows/for...
Hope that helps.