Windows 10 on external SSD - touchbar and track pad issues 2018 MBP 15". 512/16/Vega 20. 

(I should have ordered a larger internal SSD, but it wasn't really up to me.)

I have the internal SSD split into two 256GB partitions for MacOS and Windows 10. These work fine.

I have a Windows-to-Go Win10 install on a Sandisk Extreme 1TB USB-C SSD. This works fine - with an external mouse and keyboard.

Without the external input devices, I'm forced to use the touch bar for function keys, etc. The touch bar doesn't change context - swapping feature keys for F1...F12, etc. - when holding the Fn key. It displays all of the feature buttons (apologies as I don't know the term for these), but all of the buttons behave as Fx keys. So, I can't change the display brightness, volume (other than via the speaker icon on the task bar), etc. 

I could live with that, but it's annoying.

The touch pad is the big issue. I can point and click. It does not however recognize two finger clicks, so I can't scroll or access a context menu.

To clarify: All of this works on the Win10 install on the internal SSD. It does not work when booting form the external drive. The internal SSD is hosting a Windows Insider version that I need for work. The external SSD has the latest public Win10 release.

Everything works fine under MacOS.

I've run the Bootcamp WindowsSupport install (obtained on this machine via Bootcamp Assistant) to get all of the drivers in place, and it claims to have succeeded. I have network, keyboard, AMD drivers and almost everything except for this odd behavior from the touch bar and the touch pad. 

Help? 

I suspect this is a driver issue, but I've not been able to install anything beyond what the Bootcamp installer provided.
The Boot Camp Windows Support Software contains files that should be exposed to the Windows installer early in the installation process. There is also software that can be installed after Windows finishes installing. You may have only preformed the after part. In other words, have you made sure all the INF-style drivers were copied to the driver store before the first reboot during the installation process.

When using the Boot Camp Assistant to install Window 10, the files contained in the Widnow 10 ISO files are copied to the same volume as the Boot Camp Windows Support Software downloaded from the internet. So when GUI Windows installer executes, the needed files (such as drivers) are extracted from Boot Camp Windows Support Software. There is no indication to the user that this happens. Also, when Windows finishes installing, the Setup.exe application included with the Boot Camp Windows Support Software executes. This is what users do see.


  Note: If the version of Window is sufficiently newer than the model Mac, then most likely the needed software will already be include with Windows. This is only a problem when the Mac is new enough that the needed software in only exists in the Boot Camp Windows Support Software.


You may want to try a normal install of Windows 10 to the external drive instead of a Windows To Go.