Hi, I'm having the same issue immediately after replacing the keyboard in my MacBook. This is the only question I could find with this specific keyboard issue, right down to the message blinking on and off in the Keyboard Accessibility menu.
In my case, I accidentally severed the track pad wire as well; I know this would have to be replaced (I'm using a USB mouse), but if I need to replace the logic board first, I think that's a bridge too far for a laptop that's already on borrowed time. I'm just wondering if there's any other fixes people can recommend first. Thank you.