I have the keyboard out and connected via USB - shorting pin S1 does nothing it seems. Running “dmesg” while connecting the USB cable gives a lot of error messages like
[ 1446.940578] usb 1-1.2: new full-speed USB device number 32 using dwc2
[ 1447.028577] usb 1-1.2: device descriptor read/64, error -32
[ 1447.224572] usb 1-1.2: device descriptor read/64, error -32
I fear I am in the Failure mode [described in this post](Bricked Keyboard Fix - #5 by SkyRanger. I hope not but I have to investigate further in the evening.