This iPhone X (Model A1865, A1901, A1902, A1903) is running iOS 12.0.1 (16A404), which may not be supported by this version of Xcode.
Can someone please send Device Support file for this or any way to run on Xcode 9.4 with any other Device Support File.
New Update for iOS 12.1 Support file device. Don't need upload Xcode.
You just need to add support file added in Xcode
You can download 12.1.16B5059d.zip from https://github.com/mspvirajpatel/Xcode_Developer_Disk_Images/releases/tag/12.1 Extract the zip and then copy 12.1 (16B5059d) folder.
Paste this folder in this path /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/DeviceSupport
Quit the Xcode and restart, it will work.