It is an add-on that can easily generate a spiral staircase with Blender.
Please install it from Preferences and use it.

[Usage/Settings]
1.It can be used from 3Dview→Sidebar→Create tab.

1. Generate stairs with “Stair Crate”.
2. Adjust the following items.
   　
   　Step – number of stairs
   　Stair size – the size of one stair
   　Height – Even if you change the vertical width between stairs and the z of the stair size, the overall height will change, so adjust after determining the stair size
   　Interval – front and back width between stairs
3. Apply the modifier used in the stair with “Apply to Stair” and make it editable. Note that you can not set materials etc. without applying (If you apply the material from the geometry node, you can set it without applying)