Ah — I’m a bit used to that. While Rockband 3 added vocal harmonies, the first two would just pick which vocals you sang. You were never singing more than one part at a time. There were some, though, that gave more attention to a backing vocalist than the primary one. It’s fine if you recognise the pitch/tone change. One that was notorious for that was Spoonman by Soundgarden. I know that Chris Cornell was the singer of Soundgarden, but at some points in the song, it follows a backing vocalist and you have to completely change your pitch and tone, though the voice you hear does not sound like it is. It’s a very tricky song to sing and it’s generally disliked except by Soundgarden fans, most of whom would rather play it on guitar. There are others — and I’m struggling to think of an example, and threw Spoonman under the bus to try to give myself more time to think, but I’m drawing a blank on names — where it straight up turns you over to backing vocals. Like I didn’t know those lines were in the song. The main singer is singing one thing and the backing vocalists are singing something else.