I had an issue with “cp: /Volumes/W10/sources/install.wim: File too large” error. I found out there are couple of things I need to do different:

First of all to erase the USB drive, I used DiskUtility app to erase as MS-DOS (FAT) with “MASTER BOOT RECORD” scheme. Note you need to select View -> Show All Devices in order to have be able to select the drive root and have the option to change scheme.

Second, on MS-DOS (FAT) allows files only up to 4 GB and newer windows version have install.wim larger, thus you need to use NTFS file system, which is tricky to use on Mac OS. Solved by downloading ISO “Windows 10, Version 1803” from https://tb.rg-adguard.net as this is the last version with files smaller than 4 GB.

All details are described here: https://medium.com/@taig/create-a-bootable-windows-10-usb-from-macos-395773d4782e