This article provides the information regarding Preemption for redundancy group 0

You cannot enable preemption for redundancy group 0. If you want to change the primary node for redundancy group 0, you must do a manual failover.

Three things determine the primacy of a redundancy group: the priority configured for the node, the node ID (in case of tied priorities), and the order in which the node comes up. If a lower priority node comes up first, then it will assume the primacy for a redundancy group (and will stay as primary if preempt is not enabled).

If preempt is added to a redundancy group configuration, the device with the higher priority in the group can initiate a failover to become primary. By default, preemption is disabled. For more information on preemption, see preempt (Chassis Cluster).

You cannot enable preemption for redundancy group 0. If you want to change the primary node for redundancy group 0, you must do a manual failover.

Refer this document for details :- Chassis Cluster Redundancy Groups