Add an item in the template "Template Module Windows generic by Zabbix" to get the OS Version.

Create an item.

Name: Operating System Caption WMI Get
Type: Zabbix Agent
Set key as: wmi.get["root\cimv2","SELECT Caption from Win32_OperatingSystem"]
Update interval: 1d
History storage period: Do not keep history
Populates host inventory field: OS (Short)