Reply to Xcode 10.0 diagnosticd high CPU w/iPhone XR Simulator I have Xcode 12.4 both iMac 2017 and MacBook Pro 2019, both machines have Catalina. The simulator and playground are very very slow, take at least 20 minutes to start on iMac 2017. But they run pretty fast on MBP 2019. Hope Apple can fix the bug. Developer Tools & Services Xcode Mar ’21