This is a well-known issue.

When you’re on a Zoom call (or any other voice call app), the system automatically switches your device’s audio into communication mode which is optimized for voice, not for high-quality stereo sound.

Effects:

• Stereo gets downmixed to mono

• High/low frequencies are cut off

• Music, binaural, or special effects often get suppressed

On web there’s no way to bypass this because the browser doesn’t have access to low level audio routing. On native apps you should have more control.