Thank you @Akos_Shapr3D and @Kristof_Shapr3D for your help and persistence in trying to figure this out. I appreciate it’s an unusual and tricky problem to solve when you don’t have access to the affected environment.
I did try completely disable iCUE (including its background service) and the problem still happened, but while I was looking at services I wondered if some any of the input-related services might be stopped on my machine.
One service called the Touch Keyboard and Handwriting Panel Service was set to manual startup and was not running. Although I don’t use any touch input devices on my machine, I tried starting it anyway (sc start TabletInputService).
Sure enough the problem was solved and my keyboard input is now recognised in Shapr3D.
I assume because the app is cross-platform it relies on this service to process input in some way? Or maybe all UWP apps do?
Either way, starting the service has resolved the problem. 