macOS: disable threaded OpenGL (unconditionally)

We can’t determine when the app will use layer-backed
views without having access to the QWindow and NSView
instance, so make the conservative choice of always
returning false for ThreadedOpenGL.

Task-number: QTBUG-74820
Change-Id: If2779b17eead78ce1929ccebc3bd8fc0eb00c4b5
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

src/plugins/platforms/cocoa/qcocoaintegration.mm

@@ -347,11 +347,13 @@ bool QCocoaIntegration::hasCapability(QPlatformIntegration::Capability cap) cons
     switch (cap) {
 #ifndef QT_NO_OPENGL
     case ThreadedOpenGL:
-        // AppKit expects rendering to happen on the main thread, and we can
-        // easily end up in situations where rendering on secondary threads
-        // will result in visual artifacts, bugs, or even deadlocks, when
-        // building with SDK 10.14 or higher which enbles view layer-backing.
-        return QMacVersion::buildSDK() < QOperatingSystemVersion(QOperatingSystemVersion::MacOSMojave);
+        // Qt's threaded OpenGL implementation does not work well for layer-backed
+        // views, where we can easily end up in situations where rendering on secondary
+        // threads will result in visual artifacts, bugs, or even deadlocks. It is
+        // not possible to determine here if the the app will be using layer-backed
+        // views (it can opt-in using SDK 10.14+ on macOS 10.4+, or by setting
+        // NSWindow flags such as NSWindowStyleMaskFullSizeContentView).
+        return false;
     case OpenGL:
     case BufferQueueingOpenGL:
 #endif