I have a Promise Pegasus 3 attached via the Thunderbolt 3 port of my iMac Pro. Under Mojave the Pegasus 3 was working fine and I could boot into Windows 10 by holding the Option Key and selecting Windows from the Startup Manager. After upgrading the OS to Catalina, I am unable to boot into Windows via this method with the Pegasus 3 attached. The boot up process simply hangs at the Windows logo and the spinning circle of white dots. If I shut down the system, unplug the Pegasus 3 from the iMac Pro, and boot into Windows 10, it boots perfectly. I can then plug back in the Pegasus 3 and it is recognized and useable in Windows. I have all the latest drivers for the Pegasus 3 installed in Windows, and on the Mac side in Catalina the Pegasus 3 works fine and causes no problems on booting into Mac OS Catalina. After several days of contact with Promise Support, they have stated that the problem is that the firmware in the Pegasus 3 is not compatible with OS Catalina and that Promise will have to develop a new firmware for Catalina. No time frame for doing this was given, but based on my past experience with Promise Support, it may be several months before they release a firmware update for the Pegasus 3 (and other Promise Pegasus raid systems) that will resolve this issue.
Thus if you are considering upgrading to OS Catalina and have a Promise Pegasus raid attached to your Mac be aware that it will probably not boot into Windows 10 from your Bootcamp partition.
Interestingly, I have VMWare Fusion installed on this iMac Pro, and by using it I can boot into Windows using the Bootcamp partition and the virtual machine, but since this type of emulation does not support the Pegasus 3 it is not seen and not useable via this route.
Thus if you are considering upgrading to OS Catalina and have a Promise Pegasus raid attached to your Mac be aware that it will probably not boot into Windows 10 from your Bootcamp partition.
Interestingly, I have VMWare Fusion installed on this iMac Pro, and by using it I can boot into Windows using the Bootcamp partition and the virtual machine, but since this type of emulation does not support the Pegasus 3 it is not seen and not useable via this route.