Apparently at the time it came out you could barely AVOID knowing she was in it? It was a massive scandal on opening night because apparently everyone was REALLY invested in Lina Lamont (who I'll admit I'm not really a fan of in other things, but then I don't watch a lot of silent film and that was her niche), and the revelation that she wasn't the one talking OR singing absolutely torpedoed her career. Wild that lipsync controversies are as old as film with sound.
BUT, on the other hand, Katherine Selden wasn't formally credited anywhere in the film itself. I have a vague impression there were contract complications with her or Lina Lamont or both? But the upshot was, even though it literally launched her career, she's not "officially" in it. And so, nowadays, it's really easy even for people who love Katherine's voice and old films to assume it's actually Lina Lamont singing!