> As an aside, I wouldn't be at all surprised if the `open` alias was added to Debian to copy (and I mean this affectionately) macOS. Otherwise `xdg-open` might have just been called `open` from the beginning.

xdg-open was called xdg-open because the name open was already taken by another Linux command - to run a program on a new virtual console. However, since virtual consoles are used far less than they once were, eventually people decided to reserve the obvious name for the common function - so open got renamed to openvt, and open became an alias for xdg-open. It also helped prevent the confusion for people coming from macOS to Linux, trying to use open and getting a completely different command instead, and then asking “why do I have to put xdg- first???”