Hello,
I’m using Kubuntu, but I think this question is valid for the official version too.
Which is the average delay between the release of a new Ubuntu version and the availability using the “do-release-upgrade” tool? At the moment I don’t see any update for Kubuntu “No new release found.” so I think there could be some delay and the update is not available at day 1
Users on interim releases [...] are prompted to upgrade within a few days of the next Ubuntu release becoming available. This prompt may happen automatically, or when checking for new updates.
From:
So just be patient … it will show up within the next days …