We can confirm that the 3.5mm plastic piece is not functioning and is meant to allow the hub to have a more secured hold onto your M1 Pro/Max MacBook laptop. This piece would not be used when the hub is connecting to a different model MacBook such as the 2020 M1 Pro/Air.

Before moving forward, could you please confirm that you've changed your audio source in system preferences?

You can use these steps to ensure audio is recognized through your Pro Hub Mini:

1. Open System Preferences2. Select Sound, then Output
3. Ensure General USB Audio Device is selected as shown below: