The “RenderingMode” or "rendermode" property of the RadComboBox not present. so is this removed and some other alternative property is present for this.
I want to set the rendering mode to native but was unable to do it.
The information about the new features, changes and backward compatibility
issues if any for all the RadControls is available on Telerik's site, section
Products > ASP.NET AJAX Controls > What's New > Release History. You can choose an appropriate RadControls version from the Release History where all the RadControls are listed along with the new features, changes and bug fixes that are added to the corresponding control.