From the list of devices and simulators, I tap on the green “eye” button and receive this message for every iOS simulator:
Display device screen failed Another device is already mirrored
What does this mean? I was able to use an Android device just fine.
Hi @pent ,
First of all, welcome to TestProject community 
Regarding the scenario, please follow these solutions that might help:
Restart the agent and reproduce the issue
This article will show you how to enable IOS simulators and fix common issues:
Using IOS Simulators with TestProject using XCode | TestProject Help Center
If you have followed all the previous solutions and the issue still occurs, please reinstall the agent and execute the test again.
Let me know if you have managed.