ENABLING ORIGINAL SOUND IN ZOOM
Normally, Zoom processes audio to render the what they feel is the best sound for multiple people speaking, but this is not the optimal setup for playing instruments (or actually for almost anything). Fortunately they also have a built in switch that removes much of their built in processing. It's called "Original Sound" and you should make sure it's enabled for any Zoom call while using either an external microphone or an instrument (live, or pre-recorded playback). They also allow you to remove the automatic level adjustment on your microphone.

HERE'S A YOUTUBE VIDEO ON HOW TO CHANGE THESE IMPORTANT SETTINGS

Here's The Original Zoom Article On Enabling Original Sound

And here are a few excerpts from that article:

ON THE ZOOM DESKTOP APP
Sign in to your Zoom App
Under Home> Settings > Audio uncheck “Automatically Adjust Microphone Volume
Finally, if you’re using an external mic or other USB audio interface, make sure that it’s selected in the Microphone and Speaker drop down menus.

Then under the “Advanced” tab, check “Show In-Meeting Options to “Enable Original Sound” from microphone”.

NOTE: Make sure you enable the in-meeting option for original sound.

Client version 4.6 or lower: Enable it in the web portal first, then enable it in the desktop client.
Client version 4.6 or higher: Enable in the desktop client.

Sign in to the Zoom Desktop Client.
Start or join a meeting.
Click Turn on Original Sound in the top-left corner.

YOU CAN ALSO TRANSMIT STEREO AUDIO IN A ZOOM CALL
Here's The Original Zoom Article On How To Use Stereo

ON A ZOOM ACCOUNT
To enable original sound for your own use, sign in to the Zoom web portal.
In the navigation panel, click Settings.
Click the Meeting tab.
Under In Meeting (Advanced), verify that Allow users to select original sound in their client settings is enabled.
If the setting is disabled, click the toggle to enable it. If a verification dialog displays, click Turn On to verify the change.
Note: If the option is grayed out, it has been locked at either the group or account level. You need to contact your Zoom admin.

ON THE ZOOM MOBILE APP
Sign out and sign back in to the Zoom mobile app.
Tap Settings.
Tap Meeting.
Tap the toggle to Use Original Sound.