Does a “mixer” that receives several usb-audio sources exists?

iConnectivity host is midi only.
Audio is on the device ports only, it’s also discontinued(iConnectMIDI4+).

Easiest solution is an Intel NUC or other mini pc and VoiceMeeter Banana/Potato.
https://vb-audio.com/Voicemeeter/banana.htm

A Raspberry Pi should be quick enough to handle a couple devices, but I don’t know of any software like VoiceMeeter.