Black outline on stairboards but nowhere else

Hi, I rendered my interior and what occured to me is that there are these strong black outlines on the “planks” of my stairs. I made those planks as separate planes, and beveled each of them. The top planks are made the same way. Also beveled. I get the feeling the outlines have to do something with the bevels but have zero idea what. The issue is most prominent on the last stair part near the ground, where light should light it directly and still there is this strong black outline. Any help would be greatly appreciated.

Yes, your bevels are breaking the normals. Add a Weighted Normals modifier, this should fix it

Thanks I give it a try

Okay it wasn’t the normals but I just realized the material added this extra stroke that made it look so weird. So it’s the material.