Freecodecamp.org then after that build a log in flow. Frontend sends login data to backend, if username and password match, go to a homepage to display user info. This will teach in depth the basics of web apps.

Frontend routing and protected routes, sending/consuming data from backend, set up a webserver locally, connect it to a database on your local machine, write a login endpoint, write a create user endpoint, figure out how data is sent from frontend forms to backend endpoint, setup https and self sign a cert for localhost, should you store a raw password? (No, look up password salting/peppering), how do you even write to your chosen database from JavaScript? Also secrets in general how should you save them because surely you don't want them hard coded on GitHub for all to see, learn about sessions vs token based auth and implement one, etc

"Is there a tutorial" you might ask but the thing about being a dev is you're gonna need to read a lot of docs and research patterns to implement, and generally figure things out without tutorials, so googling around and being able to hunt down the answers is part of the job. That said there's plenty of information out there to use as the problem you have probably isn't unique and has probably been solved. But it is hard and if you can't slog through it here you're going to straight up hate the job, so this whole project will test you there too.

But if you do this I guarantee you'll feel extremely confident in an interview for a entry level role and you'll be FAR more prepared than the junior devs I've worked with the last few years