That's a great point. Lots of people think that full-stack means knowing how to use npm to install tailwind and express. They just don't know what they don't know.
A "full-stack engineer" should be very familiar with standards like TCP/IP, HTTP headers, the OSI model, CSS things like flexbox, DOM, CORS, SQL, websockets/eventsource, unicode etc etc as well as probably multiple web frameworks in multiple languages, various backend and cloud platforms (at least enough to get around in) like AWS and GCP, and understand what proxies and TLS are and what they do, and probably also how to do things like Let's Encrypt and write secure code with XSS, CSRF, etc hardening.
Obviously, everything is a gradient, and nobody is perfect with everything (as well as the JS build tool of the week) but this stuff takes years and perhaps decades to really grok. There's nothing wrong with being a "junior dev", or just a "dev", or whatever -- it takes a lot of effort to master your craft, especially when you're crossing multiple domains from front-end to back-end to security to architecture. But it is important to know where you best fit in, at least at whatever your current career stage is.