I know that the interim releases had issues with zfs and trying to update gave the message "Sorry, cannot upgrade this system to 25.04 right now System freezes have been observed on upgrades to 25.04 with ZFS enabled. Please see https://wiki.ubuntu.com/PluckyPuffin/ReleaseNotes for more information. "
The release notes don't seem to mention zfs. I hope these issues have been fixed?
Just FYI - That defect only impacted systems which boot from ZFS - mine did not.
The installer would stop an upgrade if it found a mounted volume - it apparently checks for zfs volumes as follows: sudo zpool list -H
I could get around the installer's ZFS check by unmounting the drive: sudo zpool export poolname
I upgraded.
Then remounted the volume: sudo zpool import poolname
Then I was up and running...