Currently, there's a known bug in iPadOS 13 and later that prevents users from using AirDrop and other share options—such as email—to share their Shapr3D designs with other devices and apps. In reported cases, the Save This File window is blank and does not display any sharing option.
Please try the workarounds mentioned in this article, "Fix Issue of 'Sharing Options Not Showing' on iOS 14/13." In many cases, you can sort out this hiccup by resetting your device's network settings.