Reason: there must be a problem with install.wim, but why?Because the size of install.wim file exceeds 4GB and exceeds the maximum support of FAT32 file system for a single file (4GB), the file is not correctly written to FAT32 format USB flash disk.

terms of settlement:

The idea of attempting to convert FAT32 to NTFS is invalid because UEFI NTFS is not supported.

Microsoft officials actually know this problem, so they also give a solution. Cut the install.wim file into two files less than 4G, and then copy it to the corresponding folder:

Delete the USB flash disk sources \ install.wim, load win10 ISO on the virtual optical drive, and run the following command with administrator privileges CMD:

dism /Split-Image /ImageFile:@:\sources\install.wim /SWMFile:@:\sources\install.swm /FileSize:3800

The first @ is modified to the drive letter of the win10 ISO virtual drive, and the second @ is modified to the drive letter of the USB flash drive, as shown in the following figure

Then you can happily and step by step to install your new win10.

However, there is a problem that the main files are not written correctly. Why is there no prompt after the UltraISO write verification process.