Why can't mockito mock my class?

I have the following service:

package inventarios.service;

import inventarios.repository.LoginUsersRepository;
import inventarios.to.LoginUser;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import java.util.List;

@Service
public class LoginUsersService {
    @Autowired
    LoginUsersRepository usersRepository;

    public List<LoginUser> findAll(){
        return usersRepository.findAll();
    }
}

And the following unit test:

import inventarios.service.LoginUsersService;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.extension.ExtendWith;
import org.junit.platform.runner.JUnitPlatform;
import org.junit.runner.RunWith;
import org.mockito.InjectMocks;
import org.mockito.Mock;
import org.mockito.Mockito;
import org.mockito.junit.jupiter.MockitoExtension;

@ExtendWith(MockitoExtension.class)
@RunWith(JUnitPlatform.class)
class GUITest {

    @Mock
    private LoginUsersService usersService;

    @InjectMocks
    private LoginWindow loginWindow = new LoginWindow();

    @Test
    void main() {
        Mockito.when(usersService.findAll()).thenReturn(Collections.emptyList());
 }
}

However when I run it I get:

org.mockito.exceptions.base.MockitoException:

Mockito cannot mock this class: class inventarios.service.LoginUsersService.

Mockito can only mock non-private & non-final classes. If you're not sure why you're getting this error, please report to the mailing list.

My class is public and it is not final. What could be wrong?