When a partial install occurs it can cause mismatched bundles across Xcode and /Library/Developer. I tried all of the following, after researching the issue for some time, xcrun devicectl manage ddis update, reinstalling XcodeSystemResources_Full.pkg, xcode-select, CLTs, clearing caches/DerivedData, deleting DDIs, resetting simulators. None worked, still got "Failed to find a DDI". Only a full removal of Xcode and reinstall fixed it. Running the 2 commands mentioned above may resolve the issue in some cases. However, from what I've seen online after replying to several threads, many people ultimately need a full reinstall. This seems especially common when Xcode was already installed and then updated to Xcode 26 via the App Store.

Hello @haptic! As @Daniel1codes mentioned in his reply to your last message, the best and easiest solution, is to carry out a full delete of Xcode, followed by a re-install from the App Store. I ran into this issue when I updated to Xcode 26, so I carried out a full delete of Xcode and reinstalled from App Store. This fixed the DDI issue. Terminal commands used to fully delete Xcode: sudo rm -rf /Applications/Xcode.app rm -rf ~/Library/Developer/Xcode rm -rf ~/Library/Caches/com.apple.dt.Xcode rm -rf ~/Library/Developer/CoreSimulator rm -rf ~/Library/MobileDevice sudo rm -rf /Library/Developer/CommandLineTools sudo rm -rf /Library/Developer sudo rm -rf /System/Volumes/Data/Library/Developer rm -rf ~/Library/Preferences/com.apple.dt.Xcode.plist rm -rf ~/Library/Application\ Support/Xcode NOTE: If you are getting 'Operation Not Permitted' when running sudo rm -rf /Library/Developer or sudo rm -rf /System/Volumes/Data/Library/Developer manually delete them in Finder.