1) For simulators run iOS14, delete folders inside ~/Library/Developer/Xcode/iOS DeviceSupport/ (folder's name started with 14.0). 2) For devices run iOS14, select Xcode window tab, click Devices and Simulators, find your device, right-click to unpair the device https://stackoverflow.com/questions/63929122/slow-app-launch-time-after-updating-to-ios-14-and-xcode-12