You’re right. Medium articles are free by default, but authors can choose to join the Medium Partner Program [0] and put one or more of their articles behind the paywall. Then when a paid member reads an article, Medium shares a portion of the revenue from their membership with its author.
I agree that Xcode increases its macOS version requirement frustratingly quickly. But I imagine Swift for TensorFlow is often used outside of the macOS/Xcode context, where you aren’t using Xcode-bundled Swift anyway. Besides, you can download a newer Swift toolchain and tell Xcode to use that. [0]
You do need to use the Xcode-bundled toolchain when archiving for the App Store, but not for development or off–App Store releases. Even for the App Store, you could get away with just one computer on your team having the latest macOS and Xcode, or with using a separate build server instead of archiving on your workstation.
[0]: https://help.medium.com/hc/en-us/articles/115011694187-Getti...