I asked Nordic the same question - in their case they use CBCentralManagerState.unknown (and perhaps a few others) to display this message. So it looks like the only workaround to detect an error is to track whether the app gets inactive within some timeout after creating CBCentralManager. If it doesn't, it means that the permission wasn't requested by iOS.

Unfortunately the issue has gone after our engineers reset network settings on the iPhone. I will report the issue when it appears again. Anyway, we would like to at least display some warning to users in similar cases, like nRF Connect does it. At the moment our app receives no error nor CBCentralStatus update after creating CBCentralManager, and it doesn't allow users to proceed, so they get stuck without any warning. Is there a way to detect unknown errors programmatically?

Attaching a screenshot from nRF Connect: