I'm recommending flask for our backend because it's lightweight (sometimes called a microframework) and doesn't have a ton of overhead to learn before diving in. If we decide to have a full database and users with profiles and logins, another framework such as Django may make more sense.
https://flask.palletsprojects.com/en/3.0.x/
https://www.geeksforgeeks.org/flask-tutorial/#
https://www.youtube.com/watch?v=mqhxxeeTbu0&list=PLzMcBGfZo4-n4vJJybUVV3Un_NFS5EOgX
What is backend engineering?: https://www.youtube.com/watch?v=XBu54nfzxAQ&t=4s
Django in >100 seconds: https://www.youtube.com/watch?v=0gT0xJ5M6Fs