The problem is, it appears that this new chip has introduced glitches on a wide variety of external audio hardware from across the pro audio industry, thanks to a bug in Apple’s software. Issues with the way the new chip synchronizes timing causes dropouts and glitches in the audio stream. (It seems basically all USB 2.0 audio interfaces will be impacted. This of course unfortunately leads users to blame their interface manufacturer, but the fault lies with Apple.)
Switching off “Set date and time automatically” in System Preferences will reduce, but not resolve the issue.
To clarify: all T2-based Macs, that is all Mac models from the 2018 generation, are evidently unusable with USB 2.0 audio interfaces, irrespective of vendor. Audio interfaces using FireWire or Thunderbolt are reportedly unaffected by this particular bug, but USB 2.0 is for the moment the most popular bus for audio devices, so nearly all owners of the new machines are encountering the issue.
I have no doubt that some users of T2-equipped Macs are seeing serious audio bugs, because USB audio has been buggy on the Mac for years, long before the T2 showed up. Even using a high-end USB interface, I get frequent pops, drop-outs and glitches when recording. Thankfully, these don’t usually end up in my recorded files, but it is annoying to hear these things while recording. And again, these problems have been present for years, making Kirn’s advice of keeping old Macs around or switching to Windows to avoid these issues just silly.
It does seem that some users are experiencing more serious issues, and clearly Apple needs to address USB audio issues on the Mac, but as a professional in the field, I can tell you, this isn’t a universal problem that makes all T2 Macs “unusable.”