xcodebuild times out when starting simulator

I have been experiencing a similar error when attempting to run an iOS app in the simulator from Xcode 11.3.1. I have found that re-choosing the virtual hardware can resolve this issue a little quicker than other solutions mentioned on this page.

When I receive the "Timed out waiting for Simulator.app to become ready" error in Xcode, the Simulator.app has typically launched but shows no actual simulator. Choosing Hardware > Device > [OS version] -> [Simulator Name] causes the simulator to appear and successfully launch my app on the next run attempt.

It seems pretty odd, but simply resetting the simulator usually fixes this. We often encounter the same error on our own CI-system.

Try Simulator-Menu -> Reset Content and Settings, then restart the simulator.

You can enforce this on the command line, but I won't recommend it, cause it will slow down your build remarkably.

There is a bug in Xcode 11.3 and earlier which could manifest this way if you have Simulator.app running from another Xcode. There is a small race window in which this could happen. That was fixed in Xcode 11.3.1.

but...

There is a bug in Xcode 11.3.1 and later (through Xcode 11.4.1 as of this comment) which manifests this way as well. To workaround the issue, you can click on Simulator.app in Dock after it launches (even if it is foreground). Alternatively, you can enable pasteboard synchronization in Simulator.app via 'Edit -> Automatically Sync Pasteboard'.