REQUIRE? no. I wouldn't say it's required -- but it HELPS!

I've said it a number of times now where as an industry we have a problem with overspecialization; artists under the DELUSION they are designers whilst not knowing anything more than how to draw pretty pictures in Photoshop, back-end developers who don't know enough HTML, CSS, or client-side JS to even be making their systems output a blasted thing, and in the middle the front end "developers" who know not enough about either to realize when the artist is handing them bloated broken inaccessible trash... much less what they should be giving to the back-end guys.

This is more true working in a full stack environment, where systems are often hobbled by bad practices and sleazily slopping together of off the shelf answers because not only are the folks at each stage barely competent enough to do their own job, they don't know enough about what those before and after them are doing in the process for their contributions to be of value.

So you SHOULD know these things -- but is it required? eh.... lots of people sneak by without it.

Not required, but it helps. If you want to work on the backend, go learn it. If you want to be a great frontender, just learn enough about backend to understand what your coworkers are doing and how to work well with them.

I think it depends on a lot of variables. How do you like your current position and company? Are you looking to replace a company soon? What are you passionate about? Front end? Everything? I would go for both in parallel. Try ngrx for one weekend and think where it can be part of your company solution, see if your boss think so too. Try spring boot. After your tried the surface of both, see what is more interesting for you.

Hope I helped, Good luck!