Technically full stack includes front end. So really it all depends on how well someone actually understands that layer. Like I know some dev-ops and some ml-ops, but to do dedicated either I'd need a fair bit of work.

Ultimately it depends on the job requirements. Some places you'd be fine just knowing react, css, typescript, etc. No matter your title if you stay on the surface like that you stay junior.

Dedicated senior front end should really understand how browsers actually work. Should be able to build various libraries and frameworks using raw js, but know to avoid that if at all possible. Should have worked with at least a few ui-frameworks. Should understand workers, sockets, events, shadow dom, css build as part of or separate from webpack build, webpack build, canvas, various common patterns for handling async like observables/promises/acid, functional and OOP, render cycles, debouncing, various local storage/cookie based ish, typescript, node, etc.

Really the main thing is about learning how to handle complex, non-linear state. Everything I mentioned is about state, and most apps need to be rearchitected from scratch because the designs are different. Unless you're working on boring stuff hahah.

Then there's all the design and UX stuff one should be at least a little familiar with.

And if you want to do web specifically there's a bunch of ish for that. You can build internal apps with the above.

>Have you experienced this kind of career change?

Hmm well I started out a barely trained full stack dev, then went nearly dedicated front end for a few years, so kinda? Front end is more complicated and takes constant work to stay on top of. That's what makes it fun. And also terrible and I'm never going back no matter how much people keep asking irl.