OTA firmrware is not rooted, and it comes with ota, but if you flash the rooted firmware, the ota function won’t work.
You can only upgrade Vroke Z1 from Android Marshmallow to Android Nougat by flashing it with PC upgrade firmware below.
Vorke Z1 PC Upgrade Firmware (root)
Vorke Z1 PC Upgrade Firmware (unroot)
Vorke Z1 SD Card upgrade firmware (rooted)