The Lord of the Rings: The Rings of Power season 1 concluded shortly after Galadriel learned that Halbrand had actually been Sauron in disguise, but she didn't tell anyone. This was a surprise since the elf had spent much of the first season trying to convince her people that Sauron was still a threat. Though she didn't have specific proof, there is a good chance that if she told Elrond such a direct claim in Rings of Power, he would have believed her. However, for some reason, she kept the information to herself.

https://screenrant.com/rings-of-power-why-galadriel-not-tell-elrond-sauron/