Yesterday the hardworking developers at The Debian Project finalized the latest version of Debian Linux, 'Bullseye' [0]. I've created a new Bullseye base image for cloud-vps and it should now be accessible in all projects.
There are likely to be bumps in the road with such a young release, but the WMCS team is committed to supporting Bullseye so you should feel confident adopting Bullseye for any new development. My cursory tests look pretty good but if you encounter issues specific to Bullseye and-cloud-vps please create a phabricator ticket or reply on the cloud list[1].
-Andrew + the WMCS team
[0] https://www.debian.org/releases/bullseye/
[1] https://lists.wikimedia.org/postorius/lists/cloud.lists.wikimedia.org/
cloud-announce@lists.wikimedia.org