I have the latest Xcode and the latest iOS on my iPhone 8.
Why am I getting this message when I run my project on my iPhone 8?
Could not locate device support files.
This iPhone 8 (Model ...) is running iOS 13.4 (...), which may not be supported by this version of Xcode. An updated version of Xcode may be found on the App Store or at developer.apple.com.
From what I read, ythat's not the first time this occurs.
Long ago as well : https://stackoverflow.com/questions/39655178/xcode-could-not-locate-device-support-files
More recent here, hope the same will do for 13.4
https://stackoverflow.com/questions/55575782/xcode-missing-support-files-ios-12-2-16e227
Those are hacks. Surely Apple has an official fix for this.
Yes, Apple wants you to upgrade your OS to Catalina to get the new XCode.