When the new Xcode can't download simulators, it's usually a permissions issue.
Solution:
Set the new Xcode as default:
sudo xcode-select -s /Applications/Xcode.app/Contents/Developer
Download iOS platform with sudo:
sudo xcodebuild -downloadPlatform iOS
If your Xcode isn't installed in the default path, update the path in step 1 to your actual installation location.
This resolves the write permission issue for new simulators.
Topic:
Developer Tools & Services
SubTopic:
Xcode
Tags: