The new app uses a different update system and will require a manual update. We're doing slow roll out to catch any issues, so we haven't added a banner for old app users yet. https://itch.io/t/295966/does-v25-need-a-manual-update
In order to update the app you'll have to download the latest version from https://itch.io/app, there is not going to be an autoupdate for version 23. Installing the new version will migrate your library and information over.