I think you can just download the source and build it as if Ubuntu didn't support ZFS. https://openzfs.github.io/openzfs-docs/Developer%20Resources... I haven't done this on Ubuntu, but I can attest that it works on Debian so unless Canonical did something "interesting" to break things it should Just Work™.
At the very least, you can do (and I have done) something similar with `apt source --build zfs-linux`. I wasn't terribly worth it for me (it takes some work?), but it's definitely possible/reasonable create backported native packages relatively easily.
