I can no longer run my app in the simulator with a version lower than iOS14. I tried iOS12, iOS12.4, iOS13.7 and they all crash with the same error. This only started since upgrading to Big Sur. Nothing has changed in my code base. This is the code that crashes:     // Provide callback audio rendering function on the unit     // Set input callback     AURenderCallbackStruct callbackStruct;     callbackStruct.inputProc = playbackCallback;     callbackStruct.inputProcRefCon = self;     status = AudioUnitSetProperty(_audioUnit, kAudioUnitProperty_SetRenderCallback, kAudioUnitScope_Input, kOutputBus, &callbackStruct, sizeof(callbackStruct) );     NSAssert1(status == noErr, @"Error setting callback: %d", (int)status);     //start audio     AudioOutputUnitStart(_audioUnit); The error "Thread 1: signal SIGABRT" occurs at the last line... AudioOutputUnitStart(_audioUnit); And the errors in the console are: /Library/Audio/Plug-Ins/HAL/JackRouter.plugin/Contents/MacOS/JackRouter: mach-o, but not built for iOS simulator 2020-11-25 15:17:34.229006-0800 PolyNome[20602:879922] Cannot find function pointer New_JackRouterPlugIn for factory <CFUUID 0x600003f11a80> 7CB18864-927D-48B5-904C-CCFBCFBC7ADD in CFBundle/CFPlugIn 0x7fbe247a7390 </Library/Audio/Plug-Ins/HAL/JackRouter.plugin> (bundle, not loaded) 2020-11-25 15:17:34.461372-0800 PolyNome[20602:880389] [AudioHAL_Client] HALB_IOBufferManager.cpp:226:GetIOBuffer:  HALB_IOBufferManager::GetIOBuffer: the stream index is out of range 2020-11-25 15:17:34.461528-0800 PolyNome[20602:880389] [AudioHAL_Client] HALB_IOBufferManager.cpp:226:GetIOBuffer:  HALB_IOBufferManager::GetIOBuffer: the stream index is out of range 2020-11-25 15:17:34.474317-0800 PolyNome[20602:880389] [aqme] 254: AQDefaultDevice (1): output stream 0: null buffer 2020-11-25 15:17:34.475993-0800 PolyNome[20602:880389] [aqme] 1640: EXCEPTION thrown (-50): - 2020-11-25 15:17:43.424327-0800 PolyNome[20602:879922] RPCTimeout.mm:55:_ReportRPCTimeout: Start: Mach message timeout. Apparently deadlocked. Aborting now. CoreSimulator 732.18.0.2 - Device: iPhone 8 Plus (796F538B-78DA-4FE7-9005-317621931E88) - Runtime: iOS 12.4 (16G73) - DeviceType: iPhone 8 Plus As I said, the only thing that's changed since it last worked is that I upgraded to Big Sur. It runs fine in the iOS Simulator, but not in simulators with a lower iOS version. The Audio Output of the Simulator is set to Internal Speakers. Any help is much appreciated.