Do Trans people have an ethical obligation to disclose they are trans to a sexual or romantic partner?

I see this argument on Twitter and I don't know how to feel. I hear that we don't tell people we're cis before sex and that only transaphobes would care. On the otherhand, I feel like that is something you should tell a partner if you're dating or having sex long-term at least. I don't know and if this is transphobic please ignore or delete.