To activate Data Storage option in WinCC Unified v18 u have to do following things.
1. Install SQL Server 2019. Create WINCCUNIFIED instance.
2. Next using SSMS In folder Security\Logins create new user NT SERVICE\WCCILScsService. I selected server roles "public" and "sysadmin".
3. In runtime settings of Wincc Unified select "Microsoft SQL" in Storage system.