Islam clearly considers homosexuality as sinful, so we cannot support it or normalize it. We don’t advocate for hatred or violence against them, and we don’t deny them human services, but we don’t encourage them or support them either. So we must avoid doing anything that supports them.
Now regarding the pronoun, if using their pronoun supports homosexuality then we should avoid it. If it doesn’t, then it’s fine. If someone doesn’t consider themselves a “he” or a “she,” and they are not openly gay/homosexual, and using a pronoun like “they” doesn’t support homosexuality, them it’s ok to use such a pronoun.