I seem to have found the solution myself. Setting .preferredColorScheme(.light) on a SwiftUI View disables dark mode.

I solved my problem by freeing up more space on my Mac by uninstalling large applications and reinstalling them after the Xcode update was successful. In the end, before updating Xcode through the App Store I had about 4x - 5x more disk space than Xcode actually needed. For anyone else I would still suggest to follow @jva´s answer, because I think that my solution was very device specific. But if nothing works I would suggest to try out freeing more space on your device.

Hey everyone, Did some of you manage to fix this? My App is out in the AppStore and sadly unusable for everyone now. I just can't figure out where to error is.

Hey Adam, did you find a solution? I came across this problem too and I just can´t figure out why it is not possible to run the ARKit Session Cam while running an AVCaptureSession.