In my case, I am using Ionic and Capacitor for app development. I couldn’t download the simulator from Xcode. What I ended up doing was downloading the Runtime manually from https://developer.apple.com/download/all/ and installing it. I realized that sometimes your Xcode version might not have a compatible Runtime available on that page because apple expect you to do this through Xcode or throught the CLI, so I downgraded my Xcode to match a version listed there. My current setup is Xcode 16 with Runtime 18. This works so I wouldn't bother upgrading for now.

I am having the same problem here. It seems this is something new. Did you manage to resolve this issue?