Check for right/middle click in Platform*.cpp

src/Platforms/PlatformXcb.cpp

@@ -90,6 +90,9 @@ public:
                         QTimer::singleShot(0, [this]() {
                             mPlatformPtr->doGrabNow(mGrabMode, mIncludePointer, mIncludeDecorations);
                         });
+                    } else if (lSecondEvent->detail == 2 || lSecondEvent->detail == 3) {
+                        // 2: middle click, 3: right click; both cancel
+                        Q_EMIT mPlatformPtr->newScreenshotTaken(QPixmap());
                     } else if (lSecondEvent->detail < 4) {
                         Q_EMIT mPlatformPtr->newScreenshotFailed();
                     } else {

src/SpectacleCore.cpp

@@ -408,9 +408,7 @@ void SpectacleCore::screenshotFailed()
         Q_EMIT allDone();
         return;
     case StartMode::Gui:
-        if (ExportManager::instance()->captureMode() != Spectacle::CaptureMode::RectangularRegion) {
-            mMainWindow->screenshotFailed();
-        }
+        mMainWindow->screenshotFailed();
         mMainWindow->setScreenshotAndShow(QPixmap());
     }
 }