If you want to generate only one single box plot for the entire matrix you can flatten the matrix into a 1D array and plot it using plt.boxplot

import numpy as np

import pandas as pd

import matplotlib.pyplot as plt

data = np.random.random(size=(4,4))

df = pd.DataFrame(data)

plt.boxplot(df.values.flatten())

plt.title("Hello Everyone")

plt.show()