Sadly, not much. My shitty job working on legacy systems doesn't really allow me to use it professionally. Still, I got a much better perspective on concurrency and systems in general, and when I occasionally see articles/videos about system design questions I could understand what they are talking about, which probably will be handy when the day arrives.

I have a colleague who suggested that I could look at open source projects on distributed systems and get my hands wet, although I haven't had a chance to do that due to time constraints. Maybe something you could consider.