OK by this: I tried deleting iOS 18 runtime via Xcode Settings > Components, and even removed iOS 26 runtime then re-downloaded it. But the iOS 18 runtime keeps auto-reappearing right after! I also ran sudo rm -rf against the iOS 18 asset folder, and it just throws a permission error—totally useless. I checked the Info.plist under /System/Library/AssetsV2/com_apple_MobileAsset_iOSSimulatorRuntime/cc1f035290d244fca4f74d9d243fcd02d2876c27.asset/ and confirmed this folder is exactly the orphaned iOS 18.0 simulator runtime. I’m trying to delete this specific cc1f035290d244fca4f74d9d243fcd02d2876c27.asset folder but hit a wall with system permissions. I found this exact issue is already being discussed in the Apple Developer Forum thread here: Orphaned 9GB Simulator Runtime in /System/Library/AssetsV2 - Cannot Delete (SIP protected). It’s clearly a bug on Apple’s side with MobileAsset lifecycle management—these large orphaned simulator runtime assets get stuck in SIP-protected system directories, and Xcode/simctl lose the ability to manage/delete them properly. The only technically workable fix (UNOFFICIAL, not recommended by Apple) is to temporarily disable SIP, boot into Recovery Mode to delete the file manually, then re-enable SIP immediately (critical for system security—never leave SIP disabled). Here’s the exact step-by-step that worked for me: Shut down your Mac completely. Boot into Recovery Mode: Press the power button, then immediately hold Command + R (for mechanical/non-Apple keyboards, use the Windows/Start key + R if Alt+R doesn’t work) until the Apple logo/progress bar appears, then release. In Recovery Mode, click Utilities in the top menu bar → open Terminal. Run csrutil disable to turn off SIP, then follow the prompt to restart your Mac. After rebooting to the normal system, open Terminal and run: sudo rm -rf /System/Library/AssetsV2/com_apple_MobileAsset_iOSSimulatorRuntime/cc1f035290d244fca4f74d9d243fcd02d2876c27.asset Enter your admin password—no more permission errors this time, and the folder deletes successfully. RE-ENABLE SIP (MANDATORY): Reboot your Mac into Recovery Mode again (repeat step 2). Open Terminal in Recovery Mode once more, run csrutil enable to reactivate SIP, then restart your Mac normally. Verify the deletion: Run ls -ld /System/Library/AssetsV2/com_apple_MobileAsset_iOSSimulatorRuntime/cc1f035290d244fca4f74d9d243fcd02d2876c27.asset—the folder should no longer exist. This is a pretty janky workaround, though. It’s ridiculous we have to disable SIP (a core macOS security feature) just to clean up orphaned simulator runtimes that Apple’s own tools can’t manage. Hoping Apple fixes this MobileAsset cleanup bug soon so we don’t have to jump through these hoops!