VMware vCenter Server 7.0
VMware vCenter Server 8.0
This issue occurs when Distributed Resource Scheduling (DRS) is enabled on the cluster. When DRS is enabled, you must change the trigger event to DRS VM powered on because DRS manages initial placement of the virtual machines.
Issue: "VM restart or VM reboot" alarm definitions are not available on vCenter Server.
As a workaround:
Refer this KB as a reference to set up alarm for VM on vCenter server.