The most common cause is the setting simply being disabled or restricted to your immediate squad.
Even with the right settings, you must be actively connected to the game's audio channel. Fix Warzone 2.0 Proximity Voice Chat Not Working
Proximity Voice Chat is a defining feature of the Warzone 2.0 experience, but it frequently glitches out due to misconfigured channels or bugged toggles. If you can’t hear nearby enemies or they can’t hear you, follow these steps to restore the audio. The most common cause is the setting simply