Python: How to show sns.catplot() in flask?

Since I'm new to Flask, I hope someone can help me fix this problem. I am not able to show my plot in Flask and I don't know what is the problem. Here is my original code:

@app.route("/")
def index():
    """ Returns html with the img tag for your plot.
    """
    return f"""
    <h1>Flask and matplotlib</h1>

    <h3>Plot as a png</h3>
    <img src="/variable.png"
         alt="random points as png"
         height="400"
    >

    """
   
@app.route("/variable.png")
def plot_png():
    """ renders the plot on the fly.
    """
    fig=Figure()
    with sns.axes_style(style='dark'):
        g=sns.catplot("satisfaction", col="Gender", col_wrap=2, data=dft, kind="count", height=2.5, aspect=1.0,
                        palette='Set3')
    plt.show(g)
    output = io.BytesIO()
    FigureCanvasAgg(fig).print_png(output)
    return Response(output.getvalue(), mimetype="image/png")