I am using winhttpcertcfg to install a certificate into "Certificates (Local Computer) / Personal / Certificates" (MMC)
winhttpcertcfg -i "C:\test.pfx" -c LOCAL_MACHINE\My -p removedForQuestion
Running this command shows the following output (no errors, but nothing suggesting it has worked either:
Microsoft (R) WinHTTP Certificate Configuration Tool
Copyright (C) Microsoft Corporation 2001.
When I search for the certificate (I checked Current User as well as Local Computer) there is nothing to see in MMC.