Headers are added in later versions of .NET Core 8 and 9 only for the Apps deployed in Windows.

• Use of Kestrel is limited only for the apps deployed in Linux App Service.

Linux App:

Also referred this Doc and tried to remove the header using the Middleware class.

• Failed to remove the header, but it is allowing to add/ update the new one.

Thanks @Thomas Ardal for the explanation.

ASP.NET Core will return the X-Powered-By header. This happens when you host your website on IIS. you simply cannot remove the header in middleware, since this is out of hands for ASP.NET Core. web.config to the rescue:

Output with Web.config:

• By default Web.config file will be created in the application root directory.
• The problem here is the setting which you updated from App Service will be removed once you re-deploy the app.

Also refer this blog for more details.