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.
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!