I have a sign on a wall that I'm trying to add neon to, but the selection also includes a selection of a wall. When I click the sign both the sign and the wall get selected, but when I click the wall, only the wall is selected. When I apply a material either way both always end up changing materials. They're separate layers--I'm able to rename each separately. I messed around in the original drawing to group the sign separately or to move it off the wall more so it doesn't think it's attached. I've tried the "apply to object vs. apply material" and nothing. It's driving me crazy.
It looks like you had the Collapse by Material option enabled when you imported your model. This takes all objects that share the same material and combines them into a single object once inside Twinmotion. To change this, you would need to go to the import settings of the imported model and then choose the Collapse all option, which will convert the model into a single object but still allow you to adjust each material individually, or the Keep Hierarchy option, which keeps each object as it was from the original design program, allowing maximum control over each particular object and materials.
