Other people more knowledgeable about stepper motors and controllers have calculated that the best layer heights to use are multiples of 0.04mm. So the recommended min is 0.08mm.
But I’ve also printed a 0.05mm layer height, and it came out nice. Next time I reprint that piece, I’ll try 0.08mm and see what the difference is.
Cura does not enforce the 0.05mm minimum layer, but I haven’t actually tried to print something. It’s happy to slice something at 0.04mm or 0.02mm.