There are tons of PowerShell scripts floating around pretending they can decode the original Windows 10 product key. Most of these scripts use outdated algorithms that no longer work in Windows 10.
Here is a much simpler way to retrieve your original Windows 10 product key:
Get-CimInstance -ClassName SoftwareLicensingService | Select-Object -ExpandProperty OA3xOriginalProductKey
If the command does not yield any return information, then there is no individual product key stored in your operating system installation.