Xcode 26.3: Simulators incorrectly shown as "build only device" — Run (Cmd+R) fails while Build (Cmd+B) and command-line build/deploy succeed

Product Xcode Version 26.3 (26C5131e) Platform macOS / iOS Simulator / iOS Device Classification Bug / Incorrect UI Behaviour Reproducibility Always (persists across restarts, scheme recreation, DerivedData clearing) Date Encountered February 20, 2026 Hardware Mac mini (M2) running macOS Test Device iPhone SE (2nd generation), iOS 26.3 Summary In Xcode 26.3, attempting to run an iOS app on any simulator destination using Cmd+R fails with the error: "A build only device cannot be used to run this target. Please select an available device or choose a simulated device as the destination." This occurs despite the selected destination being a valid iOS Simulator (not a "build only" device). The same project builds successfully using Cmd+B within Xcode and builds, installs, and runs correctly via the command line using xcodebuild, xcrun simctl, and xcrun devicectl. Steps to Reproduce

1. Open a valid iOS project in Xcode 26.3. The project in question has target name "h", product name "DiabetesHbA1cPrediction", bundle identifier "com.diabeteshba1c.DiabetesHbA1cPrediction", with IPHONEOS_DEPLOYMENT_TARGET set to 26.0.
2. In the scheme/destination picker toolbar, select any iOS Simulator destination (e.g. iPhone 16, iPhone 17 Pro, or any other available simulator). The destination name appears correctly in the toolbar without any "build only" annotation.
3. Press Cmd+R (Product > Run).
4. Xcode immediately displays the error: "A build only device cannot be used to run this target."
5. Press Cmd+B (Product > Build) instead. The build succeeds with no errors.

Expected Behaviour Cmd+R should build and launch the application on the selected simulator, just as it does in previous Xcode versions. The user had been running simulators successfully for the prior week before this issue appeared. Actual Behaviour Xcode refuses to run the app, treating every simulator destination as a "build only device." The error appears instantly upon pressing Cmd+R, before any build activity begins. Cmd+B succeeds normally, confirming the project and scheme configuration are valid. Workarounds Attempted (All Failed) The following troubleshooting steps were performed, none of which resolved the Xcode UI issue:

1. Changed IPHONEOS_DEPLOYMENT_TARGET across multiple values (26.2, 18.0, 26.0) in all build settings within project.pbxproj.
2. Deleted and recreated the Xcode scheme (removed .xcscheme files from xcshareddata and xcuserdata, let Xcode auto-create a new scheme).
3. Deleted the entire DerivedData folder (rm -rf ~/Library/Developer/Xcode/DerivedData).
4. Selected multiple different simulator destinations (iPhone 16, iPhone 16 Pro, iPhone 17 Pro) — all produced the same error.
5. Verified the scheme’s Executable setting (confirmed it was set to the correct .app target).
6. Changed "Show Run Destination" setting between Automatic and Always.
7. Quit and restarted Xcode completely.
8. Confirmed that simulator device names in the destination dropdown appeared normally, without any "build only" suffix.

Working Workaround: Command-Line Build and Deploy The project builds, installs, and runs correctly when using command-line tools, confirming the project configuration is valid: Simulator deployment: xcodebuild -scheme h -destination 'platform=iOS Simulator,name=iPhone 16' build xcrun simctl boot 7F0DF8DA-E4A3-41B2-A2E4-B1F528753189 xcrun simctl install booted <path-to-built-app> xcrun simctl launch booted com.diabeteshba1c.DiabetesHbA1cPrediction Result: App launched and ran correctly in the simulator. Physical device deployment (iPhone SE 2020, iOS 26.3): xcodebuild -scheme h -destination 'id=00008030-001128DC2E51402E' build xcrun devicectl device install app --device <device-UDID> <path-to-built-app> xcrun devicectl device process launch --device <device-UDID> com.diabeteshba1c.DiabetesHbA1cPrediction Result: BUILD SUCCEEDED, app installed and launched on the physical device without issue. Key Observations The disconnect between Xcode’s UI-based Run (Cmd+R) failing and the command-line build/deploy succeeding with identical configuration strongly suggests this is an Xcode IDE bug in the run destination resolution logic, not a project configuration issue. Cmd+B succeeds in Xcode itself, meaning the build system correctly recognises the project, scheme, and destination. The failure occurs specifically in the “run” pathway where Xcode evaluates whether the destination supports execution. The simulator dropdown shows destination names without any "build only" label, yet Xcode internally treats them as build-only when the Run action is invoked. This behaviour started occurring in Xcode 26.3. The same project and simulators worked correctly in the preceding week under the same Xcode installation. Environment Xcode version: 26.3 (26C5131e) macOS: Running on Mac mini (M2) iOS SDK: 26.3 Available simulator runtimes: iOS 18.6, iOS 26.2 Physical test device: iPhone SE (2nd generation), iOS 26.3 Project type: SwiftUI iOS app with HealthKit integration Signing: Automatic, with valid provisioning for both simulator and device