By default, Windows 10 decreases the volume of all other programs when it detects that you are in a VoIP call. Unfortunately, this detection is not very accurate. It will kick in if someone in the same room as you in Spot turns on their microphone — even if they’re in a different spatial audio zone.

This curious Windows “feature” was removed in Windows 11, so you only need to keep reading if you are using Windows 10.

To fix this issue:

1. Search for Control Panel from the Start Menu.
2. Open the Sound settings.
3. Switch to the Communications tab.
4. Select the “Do nothing” option:

(Source: Alphr)

For more information, see this article.