Try

app.py

@@ -216,7 +216,7 @@ with gr.Blocks(theme=gr.themes.Soft(text_size=text_md), css=custom_css) as main:
                 with gr.Row():
                     category_of_tasks = gr.Dropdown(
                         choices=[leaderboard_server.tasks_category_overall] + list(leaderboard_server.tasks_categories),
-                        value=leaderboard_server.tasks_category_overall,
+                        value=list(leaderboard_server.tasks_categories)[0],
                         label="Category of benchmark",
                         interactive=True,
                     )