I recently transitioned to a "full-stack dev" role (using React on FE), and honestly, it is much _simpler_ than I expected. I had the opinion before that FE is lacking the breadth of BE development, but of course, without actual experience in the matter I might have missed something.
Now that I'm 2 months in, I still don't see the complexity, actually, if anything, React makes stuff so much _simpler_ due to its leaning heavily towards FP (to me, the class-based approach of React seems more complicated than the hook-based, for example, deciding what `this` points to at any given time in Javascript is no small feat - with functions/closures, you don't have this problem). There is depth for sure, handling all the possible errors and edge cases requires care and attention, just like in the BE.
To me the only shock so far was how low level all the stuff is, I mean come on, we had Delphi in the past millenium already, creating a form with a text field and connecting it to a field in a data structure was a solved problem back then... a "one liner" if you will, now you have to independently manage the state and handle events for each field? Come on, there must be a higher level library that solves this!
FWIW if you're using hooks and React, React Hook Form is good: https://github.com/react-hook-form/react-hook-form