ZFS as a whole, has a couple components, like the actual apps / tools one uses to manipulate and actually use the filesystem, as well as the data format on the disk.
Rather than EXT4, where the tools are already in the kernel / distro, the ZFS tools are kind of separate.
It’s not a bad thing, but something that makes me use a separate, disposable boot drive on extx, and all my data on ZFS arrays (where practicable)
One can do ZFS on root, but any mis-match between kernel version and the ZFS tools needed to interact with the version, might make the system unbootable temporarily. it is rare, but can happen.
I rather just avoid it, but one can for sure recover from it.