The way to give night orchids in Baldur's Gate 3 is during the conversation with Shadow Heart. You can only give him night orchids when an exclamation mark appears in Shadow Heart.
Answer: Gifts will be given during the conversation with Ying Xin.
In the game, the player first has a conversation with Ying Xin, and chooses the first option during the conversation.
Then choose the first option in the conversation and continue the conversation with her.
After the conversation is completed, the night orchid can be given to Shadow Heart, and the potion formula can still be unlocked.
Only when the exclamation point appears in the shadow heart, you will be given a night orchid.