Thank you for your reply, what I understand here is "must be installed to eMMC via sd card (not via usb download mode)". What I want to do is to install Windows Iot to SD card, similar to partitioning SD on PC, deploying system to SD card, then inserting SD card on imx8mm and booting iot system in SD card.
I saw that Raspberry Pi has a description of installing WindowsIoT to SD card, so arm64 should be able to boot the Iot system on SD card, but I don't know how to implement it on imx8mm.