Apt completing successfully is not the same thing as the installation completing successfully. For example, Apt could successfully update a bunch of libraries,

Apt completing successfully is not the same thing as the installation completing successfully. For example, Apt could successfully update a bunch of libraries, versions, etc. which now breaks your application, but because apt's actual tasks succeeded the snapshot gets removed and now you can't roll back. > and hopefully only your rootfs; such a technique would effectively require moving all user-mutable data to other mounted volumes I believe that zfs installation creates a separate dataset for /home, meaning that it won't be rolled back along with everything else. The same should be true for things like /var/lib/, but I haven't done such an install in a while, since the first 20.04 build with zfs enabled.