left ctrl key not working on my X1 carbon

The left Ctrl key on my X1 Carbon 7th gen is not working. There are dozens, if not thousands of similar reports on google, but nothing helps:
I restarted my computer – often
OSK shows the key is working
There are no windows updates pending
I uninstalled all HID drivers, no effect
Any ideas, apart from recycling the laptop and taking my loss?