The command Set-SPLogLevel 'EventSeverity Error' is used to set the logging level for Unified Logging System (ULS) logs in SharePoint, not for the Windows event log. To configure the Windows event log to only write events that are equal to or more severe than the Error level, a different approach would be necessary, such as changing the diagnostics logging settings in the SharePoint Central Administration or using a different PowerShell cmdlet targeting the event log specifically.