UPDATE 5/24/2022 - To the best of Plugable's knowledge, the unexpected behavior described below has been resolved by the macOS 12.4 update.  While the issue has been resolved, the information below has been retained for historical reference. 

Plugable’s products based on DisplayLink technology have the ability to send an audio signal out via their 3.5mm analog audio jacks or via their HDMI or DisplayPort video output ports (which can also carry an audio signal). 

Examples of Plugable products based on DisplayLink technology are the UD-3900, UD-6950Z, or USBC-6950U. Any Plugable product based on DisplayLink technology will have a 'DisplayLink' logo printed somewhere on the product. If a Plugable product does not have this logo, then it does not use DisplayLink technology.  

In some cases, when DisplayLink-based products are used with a Mac running macOS 12 Monterey the audio signal may not be heard when switching to the DisplayLink-based device.  

This behavior appears to be tied to the order in which an audio output device is selected and used within macOS. For reference, the macOS driver used for the audio device within any DisplayLink-based product is provided by Apple and built-in to macOS.   

To expand further, consider the following two examples:

‘Working’ example

1. A Mac system is powered on with a DisplayLink device already connected. 
2. The DisplayLink device is set to the default audio output device within the ‘Sound’ macOS System Preferences application. 
3. An application plays a file that contains audio. 
4. The audio signal is heard properly via the DisplayLink device.

‘Not working’ example

1. A Mac system is powered on without a DisplayLink device connected
2. The Mac’s built-in audio output device is set as the default audio output device within the ‘Sound’ macOS System Preferences application. 
3. An application plays a file that contains audio. 
4. The audio signal is heard properly via the Mac’s built-in audio output device.
5. A DisplayLink device is connected to the Mac
6. The default audio output device within the ‘Sound’ macOS System Preferences application is changed to the DisplayLink device.
7. An application plays a file that contains audio. 
8. An audio signal is NOT heard via the DisplayLink device. 

At this time, there are three potential workarounds for this behavior:

• Restart the Mac
• Completely close the application that is affected by the behavior, and then restart the application
• Execute this command from within the macOS Terminal application (without the quotes) -->  'sudo killall coreaudiod'