How would you design a test that only a human can pass, but a bot cannot?
Very simple.
In every area of the world, there are one or more volunteers depending on population / 100 sq km. When someone wants to sign up, they knock on this person's door and shakes their hand. The volunteer approves the sign-up as human. For disabled folks, a subset of volunteers will go to them to do this. In extremely remote area, various individual workarounds can be applied.