A modern staircase you can combine differently and apply different materials to the defined surfaces areas. See the examples in Unreal, you simply pull other materials on the model’s surfaces and get as many variations as you like.
More details and the download link here, you can take it for free or pay what you like as appreciation:
Modern staircase (gumroad.com)
More assets, some free, on my Patreon site: Asset Creator is creating Game assets: 3D models, 2D materials, functionalities and more. | Patreon