Snap packages have a base. Currently the only two supported bases are core16 and core18.
LXD currently uses core18 which is based on Ubuntu 18.04 LTS.
core20 should release soon and once it does we will start moving onto it starting with the edge and beta channels. After a few months of that, we’ll look at rolling it out to stable users.
That last step can also take a few months on its own as we need to align base changes with other popular snaps that are included in distribution images to avoid wasting space by having half the pre-installed snaps use one base and the other half another.
Is there no option on recent Ceph for backwards compatibility of clients?