I ctrl-click to select multiple actors in the scene and then try to drag-n-drop a material but it only affects a single object instead of the whole selection.
Select the material in Content Browser then select the meshes in the level. And then insert the material to the meshes’ material slots in the Details panel.
The thing is, these are not BSP boxes, these are static meshes, you cannot ctrl-pick faces on static meshes.
This is working, I like how the details panel grouped objects by materials, which is very convenient!
Yup works! thank the devs, there is a way