My personal choice of language/framework right now is Python with Django. I'm aware that JavaScript and TypeScript would be more "appropriate" given my background, I want to get exposure in another language.
And to clarify, the question isn't only about languages and frameworks, but subjects and principles.
Best of luck in your transition!
Finding a job in backend will be more work than studying, but studying won't change that because finding a job is a matter of people you know + people you meet and you will still have zero work experience in backend.
Good luck.
At your current position, you may be able to start doing some work on the backend as well, maybe tell your immediate manager that you'd like to test the waters in backend as well.