What Are the Most Profitable Side Hustles for Engineers in the US?

I’ve been exploring different ways to make extra income outside my day job, and I’m curious what side hustles have worked well for others, especially fellow engineers. Freelancing in CAD design or coding seems obvious, but I’m wondering if there are less saturated options maybe niche consulting, creating digital products, or even something totally outside tech. What’s been the most rewarding or profitable for you? Any tips on getting started without burning out?