Instructions here have you creating a symbolic link between the Xcode developer folder and a root level developer folder. I don't know who thinks creating symbolic links to the root level is a good idea, but it breaks toolchains. For example, Android Studio, Google Cardboard, and a host of other products in the past have all placed symbolic links to various things at this location, with the same name.

This has never been an acceptable or good idea

On some earlier versions of MacOS, this is an actual folder with other tools located inside it.

Is there really no other way to make this work, other than a symbolic link to a 'Developer' folder at the root?

https://docs.opencv.org/master/d5/da3/tutorial_ios_install.html