https://learn.microsoft.com/ru-ru/dotnet/api/system.componentmodel.designerproperties.isindesignmode?view=windowsdesktop-10.0&redirectedfrom=MSDN
DesignerProperties.IsInDesignMode Attached Property (System.ComponentModel) | Microsoft Learn
Gets or sets whether a DependencyObject is running in the context of a designer.
property systemattachedmicrosoftlearn