Hi there,
As recently as yesterday (12/21/20), I was able to use Sonic Studio III on my Zephyrus Duo to EQ the audio on my external Acer gaming monitor.
Now, today (12/22/20), It tells me the same thing it tells the OP, 'basic mode does not support the current default audio device'!
It was just working amazingly yesterday, so what the heck is going on?