There’s some more info in the spec:
And Linux Containers - LXD - Has been moved to Canonical
At the moment its only enabled at the pool level for new instances, or on a per-custom volume basis.
We will be adding the ability to control it on a per instance basis soon so keep an eye out for that in future releases.
You can do that to a single instance, creating a zvol storage in a existing dataset like I described in a message above:
lxc storage create zvol zfs source=rpool/zvol volume.zfs.block_mode=yes size="20GB" volume.block.filesystem="xfs" volume.block.mount_options="usrquota"
lxc launch images:debian/11/amd64 debian11zvol -s zvol