My BootCamp sits on a PCiE eSATA connected SSD considered "external" by the system. This works fine on Mojave with Full Disk access following the KB on modifying the vmdk to access the boot sector.
Up to beta 8 this failed using 11.1 with SIP enabled. It started working in B8. I just updated to 11.1 and it is failing.
Could it be it needs entitlements to access external disks?