I think I have the same issue, and some folks here do to: https://developer.apple.com/forums/thread/679098?page=1 It appears that on macOS 11.3 and 11.3.1 dyld and app launch is incredibly slower for simulators while a debugger is attached. In my case I'm able to get the app to eventually launch (4-5 minutes), but once it does the debugger immediately disconnects with IDEDebugSessionErrorDomain, Code 4. I'm going to file a Radar, I recommend you do also.