We have a solution to properly send stereo audio into Zoom using Source-Nexus, see the following set up guide.
How to Send Stereo Audio into Zoom using Source-Nexus
Basically, there are several settings in Zoom that need to be configured a certain way, and then in order for Zoom to properly send the stereo signal, the input audio device to Zoom needs to be 2 channel only. If the input audio device has more than 2 channels, Zoom will only send mono.
Recordings made in Zoom will still be mono only.