System design interviews terrify career changers. "Design Twitter" sounds impossible when you've never built anything at scale.
Good news: junior and mid-level roles have different expectations. You're not expected to design Netflix's architecture. You're expected to show you understand basic concepts and can think through tradeoffs.
I'll cover what you need to know, how to approach these questions, and how to discuss tradeoffs without years of experience. The bar is lower than you think.