Kubuntu Hirsute Hippo was announced on April 22, 2021 with 9 months support.
As of January 20, 2022, 21.04 reached ‘end of life’.
No more package updates will be accepted to 21.04, and it will be archived in the coming weeks.
You can read the official end of life announcement for Ubuntu as a whole.
Kubuntu 20.04 Focal Fossa and 21.10 Impish Indri continue to be supported.
Users of 21.04 can follow the Kubuntu 21.04 to 21.10 Upgrade instructions.
Should for some reason your upgrade be delayed, and you find that the 21.04 repositories have been archived, instructions to perform a EOL Upgrade can be found on the Ubuntu wiki.
Thank you for using Kubuntu 21.04 Hirsute Hippo.