Windows 10 IoT LTSC 2021 is intended to be used by device manufacturers build embedded/IoT systems. The licensing for Windows 10 IoT LTSC 2021 is different than Windows for desktops. Pieces of Office can be installed in support of the application, but the full Office suite for Windows 10 IoT LTSC 2021 to be used a generic computer is not allowed.
Please contact a Microsoft distributor for more information: https://learn.microsoft.com/en-us/windows/iot/iot-enterprise/windows-iot-distributors?source=recommendations