We don’t have a central service that provides update information. We don’t have an check for updates mechanism because that could be used for tracking(as example an ISP could track when you started DC if we would contact a known server to check for updates on startup).
There was also an idea of sending a version code in the header in every message, but not only does this increase message size, it also could be used to find out whether a target has a specific old version that may contain a critical bug.
For the users that use an appstore the problem does not exist, because DC gets updated whenever the user decides to update all apps.
For our other users/Generally I suggest that DC send the user a device message after X days that says that a new Version might be available and links to get.delta.chat.
That way we are reminding our users with super old versions to update.
This could be implemented either only in desktop or even into the core?