I tried to install Windows 10 (1809) on a 2018 Mac mini using a USB stick I set up according to the instructions on the twocanoes site (https://twocanoes.com/create-a-windows-10-bootable-usb-flash-drive-on-a-mac/).
Downloaded bootcamp drivers with Bootcamp Assistant on the Mac mini, W10 1809 iso file from MS site, added AutoUnattend.xml to top level of the USB stick. No problems booting from USB stick, W10 installer runs fine until selecting the drive partition on which to install Windows. I created a 200GB exFat partition on the mini’s internal SSD (not a new volume within an APFS container), but after formatting this partition in the W10 installer, when I select that partition for installing W10, I get an error message saying something to the effect of “Could not create a new partition or find an existing partition”. SIP is disabled on the Mac mini. Using FAT partition instead of an exFAT one doesn’t change things.
Any ideas? Is a driver or something else missing?