plotters | rust drawing library for high quality data plotting | Graphics library

You are using std::make_unique wrong. The argument to std::make_unique is passed to the constructor and it calls new internally. You should use std::make_unique(PD)

The main problem is that the hover event gets triggered by the line instead of by the nearby scatter dots. So, this line should be excluded when connecting the motion_notify_event.

Since ImportanceOfBeingErnest's and others posts about how to create annotations, they developed the mplcursors library to strongly simplify the creation of this kind of annotations.

With mplcursors you can simply call mplcursors.cursor(ax.collections, hover=True) and automatically an annotation with x and y positions would be created. But easily can go much further. The example below also shows how to display the artist's label (here the 'artist' is one collection of scatter dots). Also, how to use the artist's color for the background of the annotation. Further, an extra attribute is added to the artist with a list of names. These names are then added to the annotation.

The code leaves out some of the elements that aren't relevant for the annotations, such as the large text.