I am on Catalina and have XCode 12 beta 6 and Safari Technology Preview installed but am getting the following :- % sudo xcode-select --switch /Applications/Xcode-beta.app  Password: % xcrun safari-web-extension-converter /Users/aarongray/Desktop/DevelopingASafariWebExtension safari-web-extension-converter requires at least Safari 14.0 to run. Unable to parse manifest.json at file:///Users/aarongray/Desktop/DevelopingASafariWebExtension I have set the Safari Technology Preview as the defualt browser but that did not help. Created as new topic :- https://developer.apple.com/forums/thread/660279

Have installed Safari 14 Beta for Catalina :- https://developer.apple.com/download/more/?=Safari