For a moment I thought you might be referring to the “GrayBox” stairs in Fortnite/GrayBox/Stairs, but it sounds like this is in the context of modeling mode.
The easiest fix would be to change your created meshes collision complexity to ‘Use Complex Collision as Simple’ - Modeling mode meshes used to be created with this setting, but that changed in 34.30. (In my opinion this was a bad change, If I’m going to create a shape I’m probably also going to want to collide with it… using complex collision (actual geometry of mesh) does have performance implications though.)