iPhone is not available. Please reconnect the device

Xcode 11.4 includes SDKs for iOS 13.4 as mentioned on the release notes here.

You must update to the beta version if you wish to deal with iOS 13.5.

Well, to be able to even get some information about why this happens, I did this:

1. Open Xcode
2. Go to windows → Devices and Simulators
3. Select your phone on the left
4. Scroll down on the right side and see the error
5. 
6. Update to latest Xcode version
7. Update you phone to the latest iOS
8. Unpair your phone from windows → Devices and Simulators.
9. Pair your iPhone
10. Enjoy

Developers who are using Xcode 11.5 and trying to install their app in iOS 13.6 device will also see this message. It's a very confusing message.

All you need to do is Download Device support files of iOS 13.6 from this link

filsv/iPhoneOSDeviceSupport

• Close Xcode

• Unzip and paste it in this location:

  /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/DeviceSupport/

• Reopen Xcode.

Now you can install the app on the iOS 13.6 device using Xcode 11.5.

Before you debug with iPhone, follow this mapping table about the version of Xcode and iOS：

Xcode 12.3 → iOS 14.3

Xcode 12.2 → iOS 14.2

Xcode 12.1 → iOS 14.1

Xcode 12 → iOS 14

Xcode 11.7 → iOS 13.7

Xcode 11.6 → iOS 13.6

Xcode 11.5 → iOS 13.5

Xcode 11.4 → iOS 13.4

Download at https://developer.apple.com/download/more/.

If you're still encountering the error, try to unpair the device within the menu Window > Devices and Simulators, clean Xcode, reconnect and trust the device, then re-run. It worked for me!

Get more info: https://en.wikipedia.org/wiki/Xcode