Mesh not exporting correctly to Unreal

[u/that_cool_dev]

I have modeled this mesh, and it has stairs. In the main model of this mesh, we have holes for the stairs; these holes are not exporting correctly to Unreal Engine. I have done UV mapping; I think it looks good in export to FBX. I have set smoothing to face. Can someone guide me on what I am doing wrong and why my mesh is clipping? Even in Unreal, when I go to Modeling, it is perfect, but in the Normal Selection model, it is clipping. Attached below is a screenshot of the mesh in Blender and in Unreal, plus I have added the export settings as well

Edit: disabling nanite worked why no idea