https://www.theatlantic.com/science/archive/2018/02/the-more...
IIRC the "less equality = more women engineers" example was India. And USSR was somewhat similar to modern India. On paper women were on par (= purely technocratic acceptance to universities) but day-to-day life was different. "Pursue your passion" was not an option. So if a girl was smart in maths, engineering it is. Fatherland needed engineers, not people in BS studies who'd work in Starbucks afterwards.
The more equality less STEM effect is seen in more than India. Sweden is the example I see talked about most. It's interesting and still heavily debated. I don't fully understand the current state of debate.
In Western Europe, where I live now, you need to look hard to find women on engineering campuses, and when you do, they're usually from abroad.