Hello Folks.

Wanted to make this post since I was able to get my 2020 MBP working with my Razer Core X and XFX AMD RX 5700 XT. I just got the Razer Core X yesterday and was unaware of the problems I would face with using it in Bootcamp (lack of research on my part). As far as I can tell, the only thing that will not work is the built in display (which isn't a problem for me). I was getting the error 12 problem until I did it this way. I did run the Ungine Valley benchmark as well as try Deep Rock Galactic which worked flawlessly.

Here are some images of proof: AMD Control Panel - Dev Management top - Dev Management bottom - Unigine Valley Benchmark

This is how I was able to get mine to work.

1. Do not have anything connected to the Macbook at all, period. Power probably would be fine, but I had nothing connected to any of the 4 ports while installing Windows.
2. Download Windows 10 image Win10_1903_V1_English_x64.iso. From many posts, this one has the pci.sys that is supposed to work with eGPUs before the changes that were made that caused the error 12 issue. I also downloaded the latest driver package from bootcampdrivers.
3. Install Windows with the ISO in Bootcamp. I chose Windows 10 Pro as I have a license for it. Let it install until the you reach the desktop. DO NOT CONNECT TO THE INTERNET.
4. Once at the desktop and you are at the bootcamp installer, turn off automatic windows updates. Copy the downloaded AMD drivers to the desktop (mine was sitting on a external USB drive). Proceed with installing the bootcamp setup. Reboot after.
5. Once back at the desktop, reboot into safe mode. Run the DDU tool included in the driver package. Check all boxes under AMD and nVidia and to prevent Windows from installing drivers. Proceed with removing all AMD and nVidia drivers in the tool (choosing not to reboot or shut down).
6. Launch device manager. Disable FaceTime camera, Bluetooth radio, the bottom 3 PCI Express Root devices and the WiFi card. Disable the Intel display adapter and reboot into normal mode.
7. Once rebooted, the display will be really laggy because we disable the driver. Connected the eGPU in the bottom left TB3 port. You should hear Windows make its connection sound followed by seeing it as a basic adapter in Device Manager.
8. Install the AMD drivers from the installer we have on the desktop. You will get the same error 207. Finish out the installer. Uninstall (and check the box to delete the driver) for the Intel card in Device Manager.
9. Reboot and profit. I did re-enable the WiFi card as well as the 3 other PCI Express Root devices. I also am able to use the eGPU plugged into the right side without issue after re-enabling the other PCI Express Root devices. You can also connect to the internet now.

Your mileage may vary but this is how I got it to work for me. As far as I can tell, updating Windows will probably break this but I am not wanting to try since it still is working even after booting into MacOS and back to Windows.