That warning message is from the Raspberry Pi firmware broadcom get_property sys interface, some user space program has read an old deprecated sys interface and is just warning to use the hwmon sysfs interface and it has no bearing on the ZFS or block WBT settings.
That warning message is from the Raspberry Pi firmware broadcom get_property sys interface, some user space program has read an old deprecated sys interface and is just warning to use the hwmon sysfs interface and it has no bearing on the ZFS or block WBT settings.