Selecting and editing text strings on Mac and Windows work in a different way.
In Windows, you click a text field, then move the input caret with the arrows. If you want to overwrite everything, you have to first select the full field.
On Mac, you click a text field, then start typing to replace the full string. If you want to only change something, you click the text string, and start moving the input caret around.
As a Mac user, I find the latest faster and more intuitive. Most often, I find myself having to rewrite full strings, instead of editing a part of them.
Maybe this behavior can be implemented in the Mac version of Dorico?