I have a Notes V11.0.1 designer client and configured a widget that imports the latest OpenNTF Domino API (downloaded from OpenNTF website) through an update site.
The plug-in is loaded in the designer

I created a new application and added the library to XSP Properties.

But when I create a simple Java class and want to import org.openntf.domino.*, I get an error:
package test;
import org.openntf.domino.*;
public class Test {
public static void test() {
Session session = null;
}
}
Error: the import org.openntf cannot be resolved. Building the app does not solve the problem.
In the MANIFESST.MF I get the following error

Any idea why this goes wrong?