In the project you’ve posted, you are listening for the binary asset to be loaded which is not the same as when the GLB binary is loaded at runtime to be added to the scene.
I’ve forked the project to do this in a way that I would do this via events.
After the GLB model is added to the scene, I fire an event on the Entity that TestFindMaterial is listening for to change materials.
Project: https://playcanvas.com/project/1022156/overview/f-load-glb-demo