2023-10-21 14:20:12.433 Xcode[6356:1443667] DVTDownloadable: Observed finish. Stop observing simulator updates. error: (null) 2023-10-21 14:25:42.218 Xcode[6356:1446770] DVTDownloadable: Download Failed. Downloadable: https://download.developer.apple.com/Developer_Tools/iOS_17.0.1_Simulator_Runtime/iOS_17.0.1_Simulator_Runtime.dmg. Error Domain=NSURLErrorDomain Code=-1001 "The request timed out." UserInfo={_kCFStreamErrorCodeKey=-2102, NSURLSessionDownloadTaskResumeData=<CFData 0x600001c0ff60 [0x1dfc4b720]>{length = 24878, capacity = 65536, bytes = 0x3c3f786d6c2076657273696f6e3d2231 ... 2f706c6973743e0a}, NSUnderlyingError=0x600001b422e0 {Error Domain=kCFErrorDomainCFNetwork Code=-1001 "(null)" UserInfo={_kCFStreamErrorCodeKey=-2102, _kCFStreamErrorDomainKey=4}}, _NSURLErrorFailingURLSessionTaskErrorKey=LocalDownloadTask .<1>, _NSURLErrorRelatedURLSessionTaskErrorKey=( "LocalDownloadTask .<1>" ), NSLocalizedDescription=The request timed out., NSErrorFailingURLStringKey=https://download.developer.apple.com/Developer_Tools/iOS_17.0.1_Simulator_Runtime/iOS_17.0.1_Simulator_Runtime.dmg, NSErrorFailingURLKey=https://download.developer.apple.com/Developer_Tools/iOS_17.0.1_Simulator_Runtime/iOS_17.0.1_Simulator_Runtime.dmg, _kCFStreamErrorDomainKey=4}

I finally got the proposed solution to work. Follow the instructions here: https://developer.apple.com/documentation/xcode/installing-additional-simulator-runtimes# Firefox will struggle to download the Runtimes as well, but until Xcode you can resume the download again and again and it will continue from where it left off last. Restart after downloading the runtime, then run the commands in Terminal.