At least on my device, it is a default behavior and cannot be altered. It was brought in with Android 8 and is same on 9 and 10.
The default USB connection mode is always charging. You need to manually enable the file transfer mode when needed.
The LAVA SimulCharge has a chip in it that detects if charge power is being supplied. If no charge power is being supplied it turns into a regular OTG connection. When it does this, it draws power from the tablet to power your accessories.
From what I've looked at so far, I haven't found a way to make the OTG 5V power from the tablet turn off when the ...
Here are some options:
Use an alternative camera app, which will allow you to set the audio source. For example: Open Camera
Record the audio in a separate app then edit the audio and video together later. An example app for recording audio from your interface is USB Audio Recorder PRO
Also, since this question is a top hit for "Pixel USB Audio Class 3", I ...