Did you take a look at this page? https://stagetraxx.com/user-guide/first-steps/
There is a short video how to import songs. When the file selector opens, just select Dropbox as the folder.
The old app was no longer maintainable. I needed lots of time to add new features because the code has grown over the years to a complexity where I would break 2 things when trying to add 1 new thing. So I really needed a new architecture.
But as you can see in the other threads I will work on the usability. Not sure which features are gone though except from the changed handling.