why clear Linux doesn’t support the OPEN-ZFS file system?
Only my guess - but most likely because it is an out of tree module. Which means it is not an official part of the Linux Kernel and is maintained out of tree separetely. This makes the support of it a bit more difficult. But as said just my guess.
Does this article help?
i know my means is want to use zfs for root device
I think only ext, XFS, and f2fs are supported by the clr installer. May I ask why you need root to be ZFS?
Unfortunatly there are propably legal reasons: OpenZFS’ CDDL license is incompatible with the Linux kernel’s General Public License. Btrfs might be an alternative?