As shown in the video, dragging a material into the landscape layers doesn’t work, nor does create/editing a landscape layer. The material being public doesn’t affect it.
Thank you for the report, the team is looking into this.
Oh yes, that is the correct behavior. Landscapes have a single Landscape Material, and inside of that material is where the layers are defined. It’s not possible to assign a material to the layer itself (though the same logic used in materials can be pasted into the corresponding layer portion of the landscape material if duplicating a given material’s appearance in a layer is desirable). The Landscape Material Blending documentation gives a good overview.
Thanks.