The actually weird thing is that my usb-keyboard shows as wakeup enabled.
grep . /sys/bus/usb/devices/*/product
outputs
/sys/bus/usb/devices/2-2/product:Mechanical Keyboard
/sys/bus/usb/devices/2-3/product:USB OPTICAL MOUSE
/sys/bus/usb/devices/usb1/product:EHCI Host Controller
/sys/bus/usb/devices/usb2/product:xHCI Host Controller
/sys/bus/usb/devices/usb3/product:xHCI Host Controller
and
grep . /sys/bus/usb/devices/*/power/wakeup
outputs
/sys/bus/usb/devices/1-1/power/wakeup:disabled
/sys/bus/usb/devices/2-2/power/wakeup:enabled
/sys/bus/usb/devices/2-3/power/wakeup:enabled
/sys/bus/usb/devices/2-5/power/wakeup:disabled
/sys/bus/usb/devices/usb1/power/wakeup:disabled
/sys/bus/usb/devices/usb2/power/wakeup:enabled
/sys/bus/usb/devices/usb3/power/wakeup:disabled
Now, I admit, my laptop setup is a little weird in that I have disconnected both the laptop screen, built-in keyboard and touchpad. I only reconnect them prior to travelling and then, only reluctantly. But that shouldn't matter because,
a) it has presented no other problems
b) when I reconnect them, waking from the usb-keyboard still doesn't work. Waking from the built-in keyboard works just fine.
I run Ubuntu 20.04.3 LTS and always avoid major under the hood tinkering if I can, if that helps. The laptop is an Acer Travelmate p256-mg.