Microsoft.PowerShell.Core\Registry
[Microsoft.Win32.RegistryKey]::OpenBaseKey
[Microsoft.Win32.RegistryKey]::OpenRemoteBaseKey

$SomeUserSID = "S-1-5-18"
$HKUTest = [Microsoft.Win32.RegistryKey]::OpenBaseKey("Users", 0)
$HKUTest.OpenSubKey( "$SomeUserSID\Environment" , $False ).GetValue("TEMP")

PS > $r.GetValue('Path','', 'DoNotExpandEnvironmentNames')
%USERPROFILE%\AppData\Local\Microsoft\WindowsApps;

PS > (New-Object -ComObject WScript.Shell).RegRead("HKEY_USERS\S-1-5-18\Environment\Path")
%USERPROFILE%\AppData\Local\Microsoft\WindowsApps;

When the GetValue method retrieves expandable string values (RegistryValueKind.ExpandString), it expands environment strings using data from the local environment. If a value containing expandable references to environment variables has been stored as a string (RegistryValueKind.String), rather than as an expandable string (RegistryValueKind.ExpandString), GetValue does not expand it. You can expand such a string after it has been retrieved by calling the Environment.ExpandEnvironmentVariables method.