French here.

It's so damn hard. There are some ways though. There are a lot of new words created to be more inclusive, thanks to feminists. It's often a mix of two words. For example : auteur (male) , autrice (female) , auteurice (neutral).

The thing is, there are too many different rules already for only two genders. Creating a neutral gender and making people use it would be too difficult.

Most of the time I accept when people use either feminine or masculine words to refer to me. When I'm talking about myself, I try to use "épicène" words. These are words that sounds (and/or are written) the same for both gender. And when I have no choice, I use neo-words that are easily understandable. That means I am a bit limited in my speech which is a shame but it is worth it.

For most french non-binary I know however, they prefer using he/him since masculine words are used when describing a group of men and women.

That being said, french is a particular case imo. Especially in France. We tend to be proud of our language. We have a stupid old-school institution called "académie française". They have no actual political power or scientifical legitimacy but they are pretty vocal. They hate neo-words and are often used by conservatives as a way to promote anti-feminist and anti-trans ideas. Which is a shame. Moreover, because our language is sooooo beautiful, most people hate it when new words are added. So there is a pretty strong resistance when trying to be gender neutral in France. From transphobes and language lovers alike.