A previous solution already proposed hide_index=True but it was incomplete. I tested this with Streamlit 1.39:

Here's the demo

Result:

Code:

import streamlit as st
import pandas as pd

df = pd.DataFrame({'N':[10, 20, 30], 'mean':[4.1, 5.6, 6.3]})
styler = df.style.format(subset=['mean'], decimal=',', precision=2).bar(subset=['mean'], align="mid")
st.dataframe(styler, hide_index=True)