This started happening to me in Xcode 12.4. I found that if I disconnected my devices the problem went away. Not a solution but a decent workaround.

Having same problem many times a day... Safari is almost unusable at this point... Constant POSIX errors and page load fails... Please Fix. I hate using Chrome.

The same iPhone works fine connected to my Macbook Pro connected to all the same networks.

Open Xcode | Settings | Accounts and make sure your session isn't expired. Fixed it for me - Xcode 14

Same problem here

Following the storyboard method here I was able to get it to work in my SwiftUI app ... https://developer.apple.com/documentation/xcode/specifying-your-apps-launch-screen