98% of what you'd be inclined to diagram out and explain for a system design interview isn't remotely proprietary. People are generally looking for a high-level overview of a system you've worked on to see a) that you've really worked on it and b) you can explain it such that it makes sense.
Sure, folks will ask you to drill down here and there for more detailed info, but if someone pokes on something where the details really _ARE_ proprietary, it's fine to just say that and offer to drill down somewhere else.
Sure, folks will ask you to drill down here and there for more detailed info, but if someone pokes on something where the details really _ARE_ proprietary, it's fine to just say that and offer to drill down somewhere else.