They play his pre-recorded vocals and he sings on top of them. But his mic volume is too low, i would say dont play precorded vocal at all, and just add maybe some harmonies.

A S D if they didn’t autotune it like crazy, they just make jon look not as talented

Without the auto tune he’s even better

I don't think it's autotune, I think that's just the music track playing under Jon singing, which was an equally foolish decision.