This is still an issue in Xcode Version 15.0.1 (15A507). I created Feedback FB13283487. The Feedback includes a sample application that replicates the issue.

I’m seeing the same “FailedToInstallAppError: Failed to install ”XCPreviewAgent.app” Could not install the preview host ”XCPreviewAgent.app” on iPhone 14 Pro” issue (with the same beta build of Xcode 15). In my case, I have a PreviewProvider declared in a file in a framework that is embedded in an app target. The current scheme is configured to launch the app.