STAIRS AND RAILS
As you can see in the above images, older versions of Blender permitted you to make your own stairs with the free plugins Archipack or Archimesh by adjusting the initial parameters when you first add it. However, in version 2.91 I noticed that the Archipack no longer works at all, and the Archimesh no longer shows deformation handle for manipulating the stair curve into a spiral staircase. It used to be that you could adjust the curvature of the steps by selecting "Include deformation handles" and adjust the spline by grabbing the few vertices on the adjustment spline. Hopefully the add that back in the future. You might want to check out this video
Blender 2.8 Easy stairs tutorial.
https://youtu.be/UZbVC9imtIg
Blender 2.8 Easy stairs tutorial.
https://youtu.be/UZbVC9imtIg