If you sound like a robot on Zoom, but not on other voice recordings, you might need to change your microphone settings to disable voice isolation.
However, the setting isn't in a very obvious place. Instead of looking in the Zoom settings, instead look for the taskbar icon that appears when the settings are open and disable voice isolation.
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I'm not sure why this causes issues—my theory is that because I'm using a cardioid microphone the lack of background noise confuses the voice isolation. In any case, turning this off fixed the issue. Hope this helps!