How to open 'This PC' using CMD or Powershell?

Just like you can run explorer.exe C:\ to open up the C: (or any other drive or folder path), you can also use a file: URI to open paths in Explorer as well. If you just specify the file: protocol without a directory (or specify file:\\), it will open This PC:

explorer file:
explorer file:\\

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Note that you can also change the default Explorer location from Quick Access to This PC as well from Folder Options:

My experience is that, the following should work:

From cmd:

Start "" "%SystemRoot%\explorer.exe" /Select,"This PC"

From powershell:

Start "$Env:SystemRoot\explorer.exe" "/Select,'This PC'"