I had the same problem, and after many trials and errors I’ve seen the light…Besides the USB connection, I’ve connected an audio OUT on my (Behringer) mixer to the “Audio in” on the rear of my computer. Also, on the DEVICES tab, I’ve chosen"line in at rear panel (blue)" as my default recording device: Edit-prefrences-devices-(interface)-recording-line in at rear panel (blue). Hope this works for you too
Don’t need a hardware workaround: there’s a Windows setting causing the mono problem … https://youtu.be/59QY0WL3f64?t=17