That is a very good question… Just checked it.
Image above is X1 probe but using X10 setting on Nano
Both stock and modified probe at 1X setting show a square wave (though with a spike on the rising edge) Change the modded probe to 10X and the wave disapears back to the first image in this thread.
I have had a couple of whiskeys, (and the screen resolution is working against me here) but its almost as if the signal is being divided rather than multiplied in this scale.
ie on a X10 probe the signal needs to be multiplied to take account of the increased attenuation of the probe but is not.
Those spikes might be the rising edge.