Благодарю за помощь!
Пример рабочего варианта
from flask import Flask
from flask_mongoengine import MongoEngine
app = Flask(__name__)
app.config['DEBUG'] = True
app.config['SECRET_KEY'] = "key"
app.config['JSON_AS_ASCII '] = False
app.config['MONGODB_HOST'] = "mongodb+srv://<user_name>:<pass>@cluster0-vkzx6.mongodb.net/<db_name>?retryWrites=true&w=majority"
db = MongoEngine(app)
from mongoengine import *
class User(Document):
description = StringField()
order_num = IntField()
link = StringField()
@app.route("/")
def index():
user = User.objects
print(user)
if __name__ == "__main__":
app.run()