Why I can't test the app on my own device even if I signed it with a valid development certificate

Thanks for the post, I would recommend to put the output of the console errors on the body of the message as well will easier to see and warning and errors to that point

The error I see at the last screen may happen when Xcode attempts to install your app onto a physical device, but the app or probably one of its embedded 3rd party frameworks lacks a valid code signature?

If you haven't set up code signing yet, the easiest way to fix this is to let Xcode handle it. Look first at the app team dropdown and make sure everything is valid. Go to the Signing & Capabilities tab and check the box for Automatically manage signing. In the team dropdown, select your Apple Developer account/team.

If your main app is signed but a third-party library or framework is not, Xcode will throw this exact error.

In General, scroll down to Frameworks, Libraries, and Embedded Content. Look at the Embed column for your frameworks. If you have dynamic frameworks like .framework or .xcframework files that are not Apple, make sure they are set to Embed & Sign. Static libraries should be set to "Do Not Embed”.

However the best way is still to looks at the warning and errors to see what framework is causing this.

Albert
  Worldwide Developer Relations.