Xcode project not showing list of simulators

Question

I open my project in Xcode 6.1. When I try to run the project, the button is grayed out. When I try to go to Product > Clean, the option is grayed out. When

Answer 1

After upgrading to Xcode 10.3, the list of simulators was empty. I rebooted and it was resolved.

This doesn't necessarily answer the OP's specific question, but this was the first place I ended up in researching my Xcode 10.3 upgrade issue.