Everyone is different. Some people who are non binary but lean/present as feminine might use feminine words, but others I’ve seen use the masculine because they think modifying the grammar is complicated.
I personally use the gender-neutral modified language, like using elle in Spanish.
I’m nonbinary, look like a woman, and use masculine grammar to mark the non-binarity − I strongly dislike the gender-neutral new language for French, but if a less cringe one arose, I’d probably use it since in English I prefer they-them :)