First, I want to say that I think you’re an awesome parent for wanting to give your kid space to explore and to support them when they deal with judgmental people out of the home. I have not had a personal experience with this so I don’t have advice but I did take this free course online that I think would help!
Health Across the Gender Spectrum | Stanford University https://www.coursera.org/learn/health-gender-spectrum
It talks about kids your child’s age and explains what is normal as well as the appropriate ways to support them. I hope it helps!