I am working with a single glb. landscape model with trees of which shadow I am trying to cast on the ground. However, I fail to produce any actual shadows on the ground.
Your concern was that receiveShadows=true was missing on the ground for the shadows to be cast on it.
Then on the mesh you getMeshByName ‘__ root __’ which was all the scene (ground too). You need to call the mesh (Tree) to add to the renderList of the shadow generator.
Open the inspector to see all the hierarchy of your glb scene