Dual read/write on the SD and MicroSD slots is not supported on the UDS-7IN1 when using DeX compatible devices. Currently, there are no available updates to provide simultaneous read/write when using the SD and micro SD ports. This is a limitation with DeX and not the hardware.
iPadOS will support dual read/write but is limited to a single process such as playing music or videos from either SD or MicroSD slot. This is a limitation with iPadOS and not the hardware.
Please note that multiplexing with the SD and microSD ports is available when using Windows or macOS.