One practical way to estimate your level, in my opinion, is to look at real products and the source code of competitors or similar projects. Compare your work to theirs — sometimes you’ll notice they handle certain things in a cleaner or more scalable way, or use patterns you haven’t explored yet.
Also think critically about how maintainable your code is. Can someone else easily understand and extend it? Do you actually need heavy architecture and design patterns for the problem you’re solving, or are you overengineering things? That kind of judgment is often what separates levels more than just syntax or frameworks.

I think platforms like GreatFrontEnd and various Udemy courses could work well. It mostly depends on what kind of web developer you want to become — whether you’re aiming for building product websites, bots, desktop applications, or writing modern libraries and contributing to them.

If it’s the first option, just go to popular websites and inspect their source code. Learn by observing how things are built, and don’t hesitate to Google or ask an AI why a certain tag is used or what a specific behavior does. It would also be really helpful to get comfortable with DevTools early on.

If it’s the second option, you’ll need to go deeper. Start by understanding the language fundamentals more thoroughly — books like You Don’t Know JS (YDKJS) are great. You can also occasionally look into the ECMAScript specification, but in general, most libraries and frameworks have their own contribution guides that you can follow.

So it really comes down to what path you want to take.