I have problems with booting to Windows 10. When I choose the Windows partition from System Preferences / Startup Disk, the machine boots to a blank screen with a cursor blinking. But if I do a PRAM reset after that, the computer boots to Windows 10 and it works. Although I would assume the PRAM reset would always boot me back to Mac (not Windows side). If I hold the Option-key at startup, I can choose the Windows partition and it will boot there normally. Although I wouldn’t want to use this method, as I have a newer GPU that doesn’t support boot screen, so I can’t use that method with that GPU (I don’t want use the old Radeon 5770 GPU and would want to move to a newer GPU). So for that reason I would want to get the System Preferences / Startup Disk method working. I found some suggestion from google about booting to Windows 10 installer CD and then running Bootrec.exe with /FixMbr, /FixBoot or /RebuildBcd, but for some reason it can’t recognize the the Bootrec-command, I don’t know if the installer can’t find the Windows partition for some reason. The Windows 10 has been installed in EFI mode. And the computer is Mac Pro 5,1 with High Sierra 10.13.4 with MP51.0085.B00 bootrom with NVME injection (so I’m booting from a Samsung 970 EVO M.2 SSD and both High Sierra and Windows are in the same disk). From Windows 10 I can boot normally to Mac, choosing the Mac partition from the Bootcamp panel.