No boot screen? No problem. Warning!: It has been discovered that Windows when installed in EFI mode is corrupting the Mac Pro’s firmware by signing it with multiple Secure Boot (X.509) certificates. Therefore Windows should only be installed in Legacy BIOS mode on the Mac Pro (5,1 and older.) Detailed information on this issue can be found within the BootROM thread. Native solution: You can switch between macOS and Windows using Apple's utilities. The latest Boot Camp 6.1 software allow you to select APFS macOS drives in the Boot Camp control panel in Windows. The Boot Camp drive is selectable in Startup Disk in System Preferences in macOS and will boot properly when installed in Legacy BIOS mode. You can use one of the 3rd party programs I've listed below if you want to, but they require SIP (System Integrity Protection) to be at least partially disabled. User h9826790 has outlined instructions here: https://forums.macrumors.com/thread...ut-a-boot-screen.2114788/page-9#post-26689280. Note that instead of deleting partitions from within Windows setup you can alternatively format the disk in macOS using Disk Utility as MBR partition scheme and select the exFAT file format. Then reformat the disk during Windows setup. Note that to format the disk with MBR partition scheme with Disk Utility you must select "View" and then select "Show All Devices." Then select the drive and click erase. Make sure you install the Mac Pro 5,1 Boot Camp software first (or whichever is correct for your system) so that all the correct drivers for your system are installed. Then, as the previously linked instructions dictate, uninstall the core Boot Camp Services and then install the iMac Pro version. Periodically Apple updates the Boot Camp software. Use the previously linked instructions to uninstall the old version and install the latest version. Note that you will not be notified when there is an update. 3rd party solutions: There are a few nifty programs that allow you to dual boot Windows and MacOS easily. There's a free one called BootChamp by Kevin Wojniak. It's a simple program that places a Windows icon on the menu bar. To boot Windows simply click the icon and then select Restart into Windows. There's another one called QuickBoot that is like a mini Startup Disk preference pane that also works from the menu bar like BootChamp. It gives you control over your macOS startup disks in addition to your Boot Camp disk. Then there is a paid program called Boot Runner by Twocanoes. It basically does the same thing as BootChamp but instead of placing an icon on the menu bar it gives you a fancy customizable boot menu that overlays the login screen. It has advanced options and is useful if you have multiple OS installations including Linux. These programs make a temporary change in NVRAM to select the startup disk so that part of System Integrety Protection must be disabled. To do that start your computer in Recovery Mode by holding command + R at startup. Open Terminal from the Utilities menu and type “csrutil enable --without nvram” and then restart the computer. BootChamp can be downloaded from https://www.kainjow.com/. QuickBoot can be downloaded from https://buttered-cat.com/product/quickboot/. Boot Runner can be found at https://twocanoes.com/products/mac/boot-runner/. There is a 14-day free trial available to new users.