The app will remain on your phone. The COVID Certificate app and the certificates it contains are stored locally on your mobile. It will therefore still be possible to display existing certificates in a reduced form even after the certificate system has shut down, as long as you do not manually delete the app. All other functions in the app are no longer available.
COVID certificates issued before 1 September 2023 and stored in the app can still be used for travel if need be, as long as they comply with the destination country’s entry regulations and their QR code has technically not yet expired. The QR code for each COVID certificate is technically valid for two years.