Hello Duccio,

You can check the status in below path in all your OS server machine.
C:\Program Files (x86)\Common Files\Siemens\ace\bin
(Please find the attached screenshot for the reference)

Redundancy between OSs are completed if "WinCC is Sync" will be checked.
Redundancy between OSs are NOT completed if "WinCC is Sync"option will be unchecked.

And,

Kindly do the configuration on the WinCC PCs as per Redundancy manual

• Inserted the Server/Client/Redundancy Licenses in respectively machines;
• Change the Project Type to 'Multi-User Project';
• Add the clients computer to the project;
• Set the Time Synchronization;
• Activate the Redundancy, set the Partner Server/Connection to partner and select the optional settings (Alarm Logging syncs and the client switch);
• Created a Server Data (Appears the name of the Physical and Redundant computers);
• Create the Alarms for Redundancy.