macOS Tahoe: Can't setup AVAudioEngine with playthrough

Hi, I'm trying to setup a AVAudioEngine for USB Audio recording and monitoring playthrough.

As soon as I try to setup playthough I get an error in the console: AVAEInternal.h:83 required condition is false: [AVAudioEngineGraph.mm:1361:Initialize: (IsFormatSampleRateAndChannelCountValid(outputHWFormat))]

Any ideas how to fix it?

        // Input-Device setzen
        try? setupInputDevice(deviceID: inputDevice)
        let input = audioEngine.inputNode

        // Stereo-Format erzwingen
        let inputHWFormat = input.inputFormat(forBus: 0)
        let stereoFormat = AVAudioFormat(commonFormat: inputHWFormat.commonFormat, sampleRate: inputHWFormat.sampleRate, channels: 2, interleaved: inputHWFormat.isInterleaved)
        guard let format = stereoFormat else {
            throw AudioError.deviceSetupFailed(-1)
        }
        print("Input format: \(inputHWFormat)")
        print("Forced stereo format: \(format)")

        audioEngine.attach(monitorMixer)        
        audioEngine.connect(input, to: monitorMixer, format: format)
        // MonitorMixer -> MainMixer (Output)
        // Problem here, format: format also breaks.
        audioEngine.connect(monitorMixer, to: audioEngine.mainMixerNode, format: nil)