I recently deleted all the LXD containers using the default BTRFS storage and the space used by the storage did not shring (according to both lxc storage info default and du -h /var/snap/lxd/common/lxd/disks/default.img there was no impact on the used space).
What’s du -sch /var/snap/lxd/common/mntns/var/snap/lxd/common/lxd/storage-pools/default getting you?
I believe btrfs is normally mounted with discard which should cause freed blocks to be released through the loop driver causing the underlying file to shrink.
Ah, the pool is a sparse file too, so ls -lh /var/snap/lxd/common/lxd/disks/default.img will show you its allocated (maximum) size but not its used size, for that, run du -h /var/snap/lxd/common/lxd/disks/default.img
I have a similar issue, I just deleted a large container (600GB), however sudo lxc storage info lxd_storage_pool_01 sudo zfs list
give that there is very little free space. (there should now be >600Gb as of my thinking)
Thank you for your help.