Cast shadows with invisible geometry

To cast shadows with an invisible geometry, you can use a MeshInstance3D with the cast_shadow property set to SHADOW_CASTING_SETTING_SHADOWS_ONLY. ¹

Things that won't work:

• A mesh that has a transparent material assigned to it, as the shadow won't work on transparent meshes. ¹
• Changing the VisualInstance3D of your geometry to be on a different layer; the shadow will ignore the geometry. ¹
• Changing light_cull_mask on the Light3D; this only changes what surfaces the light appears on. ¹