Is describing a non-Muslim or Christian Arab actress who appears in foreign films or series as an adulteress considered slandering chaste women, even if she does not commit adultery on screen but merely acts, and she is unveiled and immodest? And if I speak this way to a man, is it considered slander?

Slander (Qadhf) is of two types: general and specific.

General slander: Accusing someone else of Zina (fornication/adultery) or denying the lineage of a Muslim.

Specific slander (which necessitates the prescribed punishment, حد): When a legally competent person (mukallaf) accuses another — who is free, chaste, Muslim, adult, or a young girl who is old enough for intercourse — of Zina, or denies the lineage of a Muslim.

Based on this, describing a non-Muslim as having committed Zina does not fall under the category of slandering chaste women (qadhf al-muhsanat) that necessitates the prescribed punishment (Hadd).