I just ran into the same issue as you guys and could resolve it with a little tinkering. I just created this account to share my findings with you and hope they’re useful for somebody.
I migrated a Windows 10 (Edu) installation with Winclone from my Mid-2015 MBP 15" (R9 M370X) to my new 16" and injected the new SSD drivers as Winclone suggested.
Could boot into the migrated installation right away but had no mouse or keyboard (internal) working.
After plugging in the USB peripherals I, at least, could interact with the system again.
Problem with installating new Bootcamp Drivers:
By clicking on setup.exe in the downloaded WindowsSupport package almost nothing happened except for some graphics updates and the infamous “ERROR” message that wrote nothing but “Bootcampservice.exe”.
So far so bad.
My steps to solve the issue:
Win+R -> services.msc -> Enter
Look for Bootcamp Service in the list and stop it (right click).
Right click again and open the properties to see where the .exe file is located.
For me it’s located at: C:\Windows\system32\BootCampService.exe
After stopping the service in the previous step, I easily could delete the exe file.
Uninstall existing Bootcamp Drivers
When I tried to uninstall the old drivers through setup.exe of Bootcamp (the new one I downloaded with the WindowsSupport stuff from Apple) the program declined the action and was referring to an older version of the software that I wanted to un/install.
So now my idea was to find the old MSI package from the existing installation and uninstall it through that.
Only problem: I originally setup the system years ago and that ancient “WindowsSupport” package and the corresponding setup.exe/MSI package was long gone.
Luckily Windows stores copies of all installed MSIs at C:\Windows\Installer - but renamed and thus cryptic.
In order to find the right MSI file, I needed to have a look into the registry (regedit.exe) and navigate to this Key:
Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Installer\UserData\ (Internal USER ID)\Products\
Here I started searching (CTRL+F) for the value “Boot” (check next search result with F3) and found the “Boot Camp Services” in a sub key of “Products” in the “InstallProperties” key.
Look out for the “Install Location” “C:\Program Files\Boot Camp”.
In the same key you find the location of the wanted MSI-File under the LocalPackage key.
As soon as the right msi file is identified, just navigate to it, right-click on it and uninstall it.
Now Boot Camp should be removed and right after that I was able to run the new setup.exe without any problems.
Only issue I still have for now is the sound output but I already ran Apple Update and currently performing a Windows Update.