a word that substitutes for a noun, in particular, a person's name; a person's pronouns does not necessarily align with their gender presentation or their gender identity; a person gets to say what pronouns they and others use to refer to them; pronouns can be fluid based on context and presentation and change over time.
Preferred pronoun can imply that this is merely what is preferred rather than what is real. Using this can reinforce the idea that someone's pronouns are a choice rather than what is true for them or it's merely a preference and that you can use whatever pronouns you'd like for them.
Preferred pronouns can delegitimise pronouns of trans and non-binary people in particular, especially when their pronouns are wrongly assumed to be different than they are or neopronouns that are less commonly known. Delegitimising their pronouns delegitimes aspects of their identity, reinforces transmisia and non-binary erasure, and leads to harm against them.
Use pronouns instead.