After hours and hours of struggling with this issue I just solved it. Here is what I did: Using Finder, got to the main XP folder and right-click it. Screenshot below. Highlight and copy the path. It will ask you if you want to copy it as a path. Do that. Then past that into the XP 12 path box in the setting of the Data Manager but MAKE SURE you add /X-Plane 12/ to what you just pasted there. Do not forget the forward slash at the end. IF the path is not perfect you can hit save all you want but it will disappear from the box and you’ll have to start over. The path must match identically. As soon as I did this the scan feature found all my add-ons and I was able to update everything. Happy days! I’m going “flying”.
Still do not understand why the Data Manager file picker box will not accept the proper path when I navigated there. Perhaps Navigraph can look into why we are forced to manually type it in.
My path looks like this:
