DesiredCapabilities is obsolete
The solution is at the end of the warning message
For use with the Java remote server or grid, use the ToCapabilites method of the InternetExplorerOptions class.
InternetExplorerOptions options = new InternetExplorerOptions();options.AddAdditionalCapability("ignoreProtectedModeSettings", true);options.AddAdditionalCapability("EnsureCleanSession", true);_webdriverIE = new RemoteWebDriver(new Uri("http://localhost:5555/"), options.ToCapabilities(), TimeSpan.FromSeconds(300));