I’ve done the backend / front-end oscillation repeatedly in my career. Some advice:
Stepwise transitions are the easiest and most employable approach, so for you, front-end => full-stack (front-end + servers / scalability / AWS / DB stuff). You remain valuable throughout the transition and can slide back if you change your mind. Many employers will agree to this migratory path. Node.js is popular enough that you might not even need to switch your primary language.
Check out the “T-shaped” model of knowledge workers / engineers - the idea is to develop depth of specialization, as well as breadth of (shallower) knowledge across related areas. This is a term managers tend to understand, and you can pitch this personal growth model at work to get permission to move in the new direction, while still providing value and having impact doing the old thing.
Also, if you can find people around you who want to learn front-end stuff, you’ll have the double opportunity of getting experience teaching your front-end replacement, while yourself learning a new technical area. If you don’t know anyone, your manager might. This tends to be easier at bigger companies or startups that are growing.