This is gonna sound even stupider, I actually got my cables mixed up and the cable I plugged into the Mac Mini thinking it was the Speakers was actually the other end of the Line In cable so audio was being sent to nowhere.
Plugged the actual Speakers cable in the Mac Mini and audio played find through the Speakers.
Re-arranged the cables back to the previous setup and the issue remains :(
I’ve tried following this guide and the one on Arch’s Wiki to no avail, but I’m sure I could’ve messed something up somewhere somehow.
I think I’ve ruled out the issue being loopback specific, because even trying to use the Line In as intended (eg: joining a Discord call with the Line In set as the microphone), no audio comes through.
The motherboard is pretty recent, recent enough that it seems it doesn’t have Linux compatible drivers for Bluetooth, so I wouldn’t be surprised if my audio issues stemmed from the same problem. That, or the motherboard doing this weird jack-to-usb bridge…