2019 16" MacBook Pro (RP5300M) [9th,6C,H] + RX 6900 XT @ 32Gbps-TB3 (Razer Core X) + Win10  

System specs

MacBook Pro 16"

Core i7-9750H @ 2.6GHZ

16GB Ram @ 2666MHZ

AMD Radeon Pro 5300M

eGPU hardware

Razer core

AMD Radeon 6900XT

Software

Windows10 20H2 - 19042.631

Radeon Software 20.12.1 (2020, Dec) - bootcampdrivers.com

Installation steps

1. Install Windows in bootcamp

2. Install the driver that comes with bootcamp

3. Turn off or pause automatic updates

4. Install the driver downloaded from bootcampdrivers, use DDU to uninstall the previous driver in safe mode before installation

     I did not uninstall the sound card driver, DDU is using the default configuration.

5. After installing the driver, reboot into MacOS

6. [EFI Loader] Error 12 Fix in Boot Camp for Apple T2 Security Chip Macs (apple_set_os loader v0.5) | BootCamp eGPU Setup Follow the steps within this post to modify the EFI file.

7. After modifying the EFI file, turn off your computer and then plug the eGPU into the left usb port.

8. your computer will automatically boot up and boot windows. you will see that the modified EFI file has taken effect, then press any key to enter the system. You will feel that the boot-up speed is significantly slower.

9. When windows loads to the desktop (you can see the icon of the application on the desktop), unplug the eGPU and reinsert the eGPU in the right usb port.

      Note that the egpu is switched from the left to the right side of the computer

10.Wait 15~20 seconds, then unplug the egpu and plug it back into the left port where it was previously plugged in.

 Notes:

You can actually use the official driver, but the dGPU won't work. Also I disabled the iGPU in Device Manager.
I updated macOS to 11.3 beta5 but still can't drive the 6900XT.