With Xcode 11, Apple removed the Application Loader app that was used to manually upload apps to the Mac and iOS App Stores. The workaround was to keep a copy of Application Loader from an older version of Xcode or to use xcodebuild from the command line instead.
Fortunately, Apple just released a new app to bring back this functionality: Apple Transporter. You can download it from the Mac App Store and use it to upload your apps.
Special thanks to Gavin Smith for being the first one to notice this and bring it to our attention.