change to update

app.py

@@ -468,7 +468,7 @@ with gr.Blocks(delete_cache=(600, 600)) as demo:
         inputs=[output_buf, gr.State(0.95), gr.State(1024)],
         outputs=[model_output, glb_download]
     ).then(
-        lambda: gr.Button(interactive=True),
+        lambda: gr.update(interactive=True),
         outputs=[glb_download]
     )