PathUnExpandEnvStrings

[DllImport("shlwapi.dll", CharSet = CharSet.Unicode)]
public static extern bool PathUnExpandEnvStrings(
   [MarshalAs(UnmanagedType.LPWStr)] string pszPath,
   [MarshalAs(UnmanagedType.LPWStr)] StringBuilder pszBuf,
   uint cchBuf
);

Microsoft documentation: Link