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Xcode 10.x.x cannot build a Swift 3.x iOS application.Xcode 9.x.x is required to perform the conversion away from Swift 3.x. Xcode 9.x.x is not compatible with Catalina 10.15.2.I am unable to locate installers for previous versions of macOS. Additionally, the hardware is a 16-inch MacBook Pro which, if I understand correctly, cannot run Mojave.What is the present-day best practice for performing a Swift 3.x conversion from the 16-inch MacBook Pro?

I am attempting to bring a Swift 3.x application up to date to the latest version of Swift by executing conversions in old versions of Xcode. This has brought me to Xcode 9.x.x. So, I attempted to install Xcode 9.x.x on a 16-inch MacBook Pro running Catalina 10.15.2. I tried both 9.4.1 and 9.3.1. Both failed with error:Dyld Error Message: Symbol not found: _OBJC_IVAR_$_NSFont._fFlags Referenced from: /Applications/Xcode 9.4.1.app/Contents/MacOS/../SharedFrameworks/DVTKit.framework/Versions/A/DVTKit Expected in: /System/Library/Frameworks/AppKit.framework/Versions/C/AppKit in /Applications/Xcode 9.4.1.app/Contents/MacOS/../SharedFrameworks/DVTKit.framework/Versions/A/DVTKitI suppose AppKit in 10.15.2 no longer possesses the symbol expected by Xcode. Am I correct to conclude Xcode 9.x.x is not supported on Catalina?If this is the case, how can I obtain a copy of High Sierra or Mojave to run Xcode from there? I understand I may not be able to run these operating systems natively on the 16-inch MacBook. Is it possible to run these older OS versions in a VM?