Color picking with Qt in OpenGLWidget

Question

I've been reading tutorials about picking and that color picking is far the most popular and simplest form.

For some reason, when I add glEnable(GL_DEPTH_TEST), the objects stop being selected correctly. When I remove this function, it selects objects normally, but there is a problem with overlapping objects. How can I fix this?

int WidgetGL::selectObject(int xx, int yy, QVector<Transformational *> &objs)
{
    m_selectBuffer->bind();

    glViewport(0, 0, width(), height());
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);


    m_selectProgram.bind();
    m_selectProgram.setUniformValue("u_projectionMatrix", m_projectionMatrix);
    m_camera->draw(&m_selectProgram);

    for (int i = 0; i < objs.size(); i++) {
        m_selectProgram.setUniformValue("u_code", (float) (i + 1));
        objs[i]->draw(&m_selectProgram, context()->functions());
    }
    m_selectProgram.release();


    GLuint viewport[4];
    GLubyte res[4];
    glGetIntegerv(GL_VIEWPORT, (GLint *) viewport);
    glReadPixels(xx, viewport[3] - yy, 1, 1, GL_RGBA, GL_UNSIGNED_BYTE, &res);
    // m_selectBuffer->toImage().save("select.bmp");


    m_selectBuffer->release();

    return res[0];
}

I tried to fix it in every way, but still nothing worked