restrict workaround to 10.13+ versions

src/desktop/UBDesktopAnnotationController.cpp

@@ -84,7 +84,15 @@ UBDesktopAnnotationController::UBDesktopAnnotationController(QObject *parent, UB
     mTransparentDrawingView->setAttribute(Qt::WA_TranslucentBackground, true);
 #ifdef Q_OS_OSX
     mTransparentDrawingView->setAttribute(Qt::WA_MacNoShadow, true);
+    /* https://bugreports.qt.io/browse/QTBUG-81456 */
+    if (QOperatingSystemVersion::current().minorVersion() > 12) /* > Sierra */
+    {
         mTransparentDrawingView->setWindowFlags(Qt::FramelessWindowHint | Qt::WindowStaysOnBottomHint | Qt::Window | Qt::NoDropShadowWindowHint | Qt::X11BypassWindowManagerHint);
+    }
+    else
+    {
+        mTransparentDrawingView->setWindowFlags(Qt::FramelessWindowHint | Qt::WindowStaysOnTopHint | Qt::Window | Qt::NoDropShadowWindowHint | Qt::X11BypassWindowManagerHint);
+    }
 #else
     mTransparentDrawingView->setWindowFlags(Qt::FramelessWindowHint | Qt::WindowStaysOnTopHint | Qt::Window | Qt::NoDropShadowWindowHint | Qt::X11BypassWindowManagerHint);
 #endif