How do I make decisions about design or technical direction when I'm not the expert?

You don't need to be the expert. You need to know what you don't know, and to think clearly about how the decision gets made. When I faced questions outside what I knew well, I learned to listen more than I talked. I'd ask the people who did know: What are you seeing that I'm not? What would failure look like here? What are you unsure about? Then I'd sit with their answers before deciding. Your gap in expertise isn't a weakness to hide. It's information. Use it. If your gut says a direction feels wrong but you can't say why, name that anyway. Sometimes instinct catches what analysis misses. Say, "I'm not sure about this yet. What am I missing?" That's a real question, not weakness. But don't fake understanding just to look decisive. A choice made from false confidence does more damage than one made slowly. Take the time to understand enough to choose. Not to become an expert, but to own the call. And when the experts disagree, and they will, your job is to weigh the stakes of each path and decide which risks you're willing to carry. That takes judgment, not technical knowledge. That's exactly where your role matters. Use it.