Not sure how much this will help, but from a UX design perspective you could look at it in one of two ways:
Be a ‘generalist’ in content design, i.e. produce content that is a combination of copy (wear the UX copywriter hat) and imagery (visual design) but apply the usual HCD and Agile methodology to fit in the bigger picture.
Be a ‘specialist’ in content design, i.e. produce more immersive content like infographics or data visualization (that can also be interactive) and apply the usual HCD and Agile methodology etc.
There are a number of online courses relating to data journalism, data science and communication that will provide exposure to theory or practice, but I don’t know anything specifically related to content design as a course.
I think the more you can develop your own experiences and methodology as a UX designer, the easier it will be to adapt it to move sideways in your career. Or else you can try and make a bigger leap from a graphic/visual designer to a content designer as well. Good luck!