On team time trials, I am on discord to hear the Captan or others.
If it is just a normal Zwift race and I don't care much, I use ear buds. They drown out the blower and trainer noise.
I really should have had a TV or bigger screen. I used a laptop and never figured out who I was racing with. I would often be in a pack of racers in a higher category and did not know it, suffering unnecessarily. A nice big TV would prevent such mistakes....or young eyes.