I've been using the BetterTouchTool for several years now (and quite happy with it), and has always been possible to "program" a middle mouse button on my Magic Mouse that works perfectly as any other mouse-with-a-real-scrollwheel. This means that I can zoom by scrolling, pan when dragging and zoom to fit in window when double clicking.
This last option no longer seems to work in Archicad 25. Any other users with the same issue? I'll be posting this in the Archicad Community as well...