It's not related to Xcode Cloud. In my case it can be observed locally or on bitrise. Xcode 16.2 iOS 18.2

It's not related to tests itself. It's a specific simulator behaviour. It can be reproduced locally if you reset simulator xcrun simctl erase all and then run it. After booting it and waiting doing nothing in my case approximately 1 minute you can observe black screen with a white Apple logo and a progress bar. My suggestion is to boot simulator before tests and give it some time to be ready for testing. Ex. xcrun simctl boot <YOU TEST DEVICE> sleep(30)

Forgot to mention - Xcode 16.2 iOS 18.2

To be sure that simulator has been booted properly use xcrun simctl bootstatus <YOU TEST DEVICE> -b