"Why does Biden look and sound fine when his campaign is shooting him on film the day after and didn't when it was the news hand of David Zaslav's company?" has its own answer if you just think about it a little bit
a simple explanation would be that they chose to keep both candidates’ mics at the same level, which would be absolutely insane in literally any other context but somehow seen as fairness in this one
also the extremely bright lights made trump's highly bronzered skin look almost normal while it made biden look like a fucking ghost. some of this is on CNN, but some of it's also on Biden's team who should have negotiated the lighting and sound.