Problems installing iOS 18.4 SDK on Intel iMac

No idea, but you could see if there are any disk images showing in Disk Utility, and eject them so they're gone. You might then be able to reinstall.

I can't confirm this will fix your issue, but that has helped me in the past.

If I try to remove that "unknown Platform Simulator" in Xcode, I get this error message:

Unable to remove SimulatorRuntime
Domain: com.apple.DVTFoundation
Code: -1
User Info: {
    DVTErrorCreationDateKey = "2025-04-05 12:46:30 +0000";
}
--
Unable to remove SimulatorRuntime
Domain: com.apple.DVTFoundation
Code: -1
--
SimulatorInfo is missing RuntimeInfo for <DVTSimulatorInfo> {
| identifier: 7E6FC6E4-F04C-4F98-BA77-AAD62F4CB8B5
| kind: 3
| sizeInBytes: 8825558354
| lastUsedAt: (null)
| state: 4
| stateDisplayString: Unusable
| canDelete: 1
| unusableStateError: Error Domain=SimDiskImageErrorDomain Code=5 "(-67061 invalid signature (code or signature have been modified)" UserInfo={NSLocalizedDescription=(-67061 invalid signature (code or signature have been modified), unusableErrorDetail=}
| userInfo: {
    DVTDownloadableIdentifier = "com.apple.dmg.iPhoneSimulatorSDK18_4";
    DVTDownloadableOperationUniqueIdentifier = "5E937CD3-1EDD-4789-B6CC-3D427A6D4DDD-5843-0000029B5534E7EF";
    DVTDownloadablePlatformIdentifier = "com.apple.platform.iphoneos";
}
| runtimeInfo: (null)
| imageURL.path: /Library/Developer/CoreSimulator/Cryptex/Images/bundle/SimRuntimeBundle-C1F1888C-8630-4D4F-8032-3F41EF54AE6B/Restore/090-44334-323.dmg
| parentImageURL.path: /System/Library/AssetsV2/com_apple_MobileAsset_iOSSimulatorRuntime/6fb1e5fe25ee1c372f7116516e615c556906bd4e.asset/AssetData/090-44150-318.dmg
}
Domain: DVTFoundation.DVTDownloadableManagerErrors
Code: 0
--


System Information

macOS Version 15.4 (Build 24E248)
Xcode 16.3 (23785) (Build 16E140)
Timestamp: 2025-04-05T14:46:30+02:00

I tried to delete the file at "/System/Library/AssetsV2/com_apple_MobileAsset_iOSSimulatorRuntime" - but the system wouldn't let me, even a sudo wouldn't help.

I tried to delete the file at "/System/Library/AssetsV2/com_apple_MobileAsset_iOSSimulatorRuntime" - but the system wouldn't let me, even a sudo wouldn't help.

simctl is the command you're looking for, with these 2 variants:

% xcrun simctl runtime list
% xcrun simctl runtime remove <identifier>

The first will help you find the identifier to use in the second. From your log message, the identifier might be 7E6FC6E4-F04C-4F98-BA77-AAD62F4CB8B5, but double check first.

— Ed Ford,  DTS Engineer

When I try the first, I get this result: [...] There is no iOS runtime installed, that I could delete …

Hmmm, that's interesting. Since there's an identifier in your error message, what happens if you pass the identifier from the error message to the remove command?

— Ed Ford,  DTS Engineer

I've run the commands you mentioned and run them in order to demonstrate my problem:

$ xcrun simctl runtime list                                           
== Disk Images ==
-- tvOS --
tvOS 18.4 (22L254) - C5A9C190-ABF9-4949-9112-D063E82ECA5B (Ready)
-- watchOS --
watchOS 11.4 (22T250) - EB2C6365-BB36-4E19-99C2-0CE20CDD3C96 (Ready)

Total Disk Images: 2 (8.5G)
$ xcodebuild -downloadPlatform iOS                                    
Downloading iOS 18.4 Simulator (22E238): Preparing to download...2025-04-11 08:07:03.506 xcodebuild[4333:39611]  DVTDownloadable: Observed finish. Cancelling download asset. {
    assetId = 6fb1e5fe25ee1c372f7116516e615c556906bd4e;
    assetIdHash = 9d684dee0a7bae81ba9c4f79475976f41789eaf3;
    assetType = "com.apple.MobileAsset.iOSSimulatorRuntime";
    attributesHash = 99e0653b3c175e32d4a045cb9be856573b2938c1;
    contentHash = d4aad730490a4476d8179d4cdb7c1fcae8dd388a;
    nonIdHash = be7dd5950580ff7c8e1f822b24bd76d58c08b8aa;
    pallasDynamicAssetIdHash = d7904ac1d93cc3702244074c49aafad923a6e2b4;
    policyHash = d3700ca0e5058eb1d7b21fd74b1c225a66f5e74e;
    urlHash = fc93246f74e44ae2b94a727bfd9bac228f69f961;
}, error: (null)
Downloading iOS 18.4 Simulator (22E238): Error: Error Domain=SimDiskImageErrorDomain Code=5 "(-67061 invalid signature (code or signature have been modified)" UserInfo={NSLocalizedDescription=(-67061 invalid signature (code or signature have been modified), unusableErrorDetail=}
$ xcrun simctl runtime list       
== Disk Images ==
-- tvOS --
tvOS 18.4 (22L254) - C5A9C190-ABF9-4949-9112-D063E82ECA5B (Ready)
-- watchOS --
watchOS 11.4 (22T250) - EB2C6365-BB36-4E19-99C2-0CE20CDD3C96 (Ready)
-- unknown --
<unknown platform> - 4C2932FD-404F-49EA-B8F4-9ED904C97F4E (Unusable - Other Failure: (-67061 invalid signature (code or signature have been modified))

Total Disk Images: 3 (16.7G)
$ xcrun simctl runtime delete 4C2932FD-404F-49EA-B8F4-9ED904C97F4E
$ xcrun simctl runtime list                                       
== Disk Images ==
-- tvOS --
tvOS 18.4 (22L254) - C5A9C190-ABF9-4949-9112-D063E82ECA5B (Ready)
-- watchOS --
watchOS 11.4 (22T250) - EB2C6365-BB36-4E19-99C2-0CE20CDD3C96 (Ready)

Total Disk Images: 2 (8.5G)
$ xcodebuild -downloadPlatform iOS                                
Downloading iOS 18.4 Simulator (22E238): Preparing to download...2025-04-11 08:11:02.639 xcodebuild[4563:45093]  DVTDownloadable: Observed finish. Cancelling download asset. {
    assetId = 6fb1e5fe25ee1c372f7116516e615c556906bd4e;
    assetIdHash = 9d684dee0a7bae81ba9c4f79475976f41789eaf3;
    assetType = "com.apple.MobileAsset.iOSSimulatorRuntime";
    attributesHash = 99e0653b3c175e32d4a045cb9be856573b2938c1;
    contentHash = d4aad730490a4476d8179d4cdb7c1fcae8dd388a;
    nonIdHash = be7dd5950580ff7c8e1f822b24bd76d58c08b8aa;
    pallasDynamicAssetIdHash = d7904ac1d93cc3702244074c49aafad923a6e2b4;
    policyHash = d3700ca0e5058eb1d7b21fd74b1c225a66f5e74e;
    urlHash = fc93246f74e44ae2b94a727bfd9bac228f69f961;
}, error: (null)
Downloading iOS 18.4 Simulator (22E238): Error: Error Domain=SimDiskImageErrorDomain Code=5 "(-67061 invalid signature (code or signature have been modified)" UserInfo={NSLocalizedDescription=(-67061 invalid signature (code or signature have been modified), unusableErrorDetail=}

However, in the end, the installation always fails …

Christian

I found a workaround to get the runtime installed on my iMac. Using a second computer which had the runtime installed, I executed the following command:

$ xcodebuild -downloadPlatform iOS -exportPath . 
Finding content...All available platforms are downloaded
Exported 'com.apple.CoreSimulator.SimRuntime.iOS-18-4' to /Users/cmittendorf/Desktop/iphonesimulator_18.4_22E238.dmg

The DMG file was copied over to my iMac and then installed using:

$ xcrun simctl runtime add iphonesimulator_18.4_22E238.dmg 
C: F5BC51BD-6280-42AE-B85B-7FA96C6C5C4A iOS (18.4 - 22E238) (Ready)