iOS 18.3.1 is just released: February 10, 2025. And as all we know that: xCode does not has option to download iOS simulator 18.3.1. I have just released a new update app version and received rejected by 1 issue from iOS 18.3.1 and reached here, and then searching download resource for iOS simulator (of course, no available). Maybe this is sync-up issue from Apple or iOS 18.3.1 is hot-fix for some critical issue which they don't want developer knows first.

+1 same issue Happened with xCode 14.3, iOS 13.x other ios version, xcode version working fine. So now I have to choose drop my user or config system to fallback to xCode 14.2 :|