main.py

from flask import Flask, render_template

app = Flask(__name__)


@app.route("/")
def home():
    return render_template('index.html')


@app.route("login")
def login():
    return render_template("login.html")


if __name__ == '__main__':
    app.run(debug=True)

There should be forward slash '/' before login
The code should be
@app.route("/login") def login(): return render_template("login.html")

Otherwise it is showing error

Yeah must be a typo, she works really hard!