Agreed. It's the concepts behind the general format of most web frameworks that's good to know. Switching from something like Django to Express will come with challenges, but those come from structure of code and what batteries are included. If you understand databases, sessions, middleware, etc, you're transition from one to the other will probably be pretty easy.

I've worked with Flask, Express, NextJS, and vanilla PHP professionally, and while they feel different in structure and ergonomics, they all do the same thing and the transition was easy.