I would be very excited about people working in cybersecurity in relation to protecting important information related to EA cause areas, such as in AI and in bio. This could definitely involve working for the US government but that could also involve working for AI companies such as DeepMind, OpenAI, or Anthropic. There may be some risks of automation- in that case, learning how to use AI and ML within cybersecurity sounds very promising.
I'm curious, given that apparently the U.S. govt is in need of people to work in cybersecurity, whether there's a good case to be made that—assuming you believe in protecting the U.S.' best interests/security—working in cybersecurity is a promising EA career choice. I'm also curious, among people who know the field at all, whether they have reason to think this field may be automated anytime soon (I've read accounts that, for this reason, IT/cybersecurity related jobs might be relatively short-lived).
While this post (on reducing catastrophic risk through a career in infosec) isn't strictly about protecting the United States (and EA, as an international community, isn't especially focused on U.S. interests), it's the most relevant one I'm aware of for your question.