I have a same issue.
Log.txt
Encountered an error communicating with IBAgent-iOS. (Failure reason: IBAgent-iOS (-1) failed to launch): Failed to launch IBAgent-iOS via CoreSimulator spawn (Failure reason: Failed to spawn IBAgent-iOS on iPhone Xʀ (F2312C83-F9CB-4D88-887A-D8CDBA090B46, iOS 14.3, Booted)): Invalid device state
TomoyaOnishi
Users receive reputation points by contributing quality content to the forums.
Posts include post and replies published on the forums.
Post authors can mark replies as Accepted to indicate successful solutions.
Apple Developer Forums admins can mark replies as Apple Recommended to indicate an approved solution
Last seen
User for
Post
Replies
Boosts
Views
Activity
I downgraded to Xcode 12.2. It works for me.
https://developer.apple.com/download/more/?=xcode
clean build, clean derived, restart Xcode/Mac, reinstall Xcode, downgrade to 12.2 doesn't help. I'm running Xcode in Downloads directory, not Application Folder. It may be related to problem. try it.
Check Target Membership of .intentdefinition file in your Widget Extension.