Without a transform in World Space:
Or, transformed into Local Space:
This is in the NPC, the way you preferred.
You can, ofc, use the widget component in world space which you already rotate. Also, no need to attach the widget to the spline. It would only make things more complicated at times.
To make it work at greater distances, in case it gets jerky, you may need to work in some interpolation.
What’s the closest point changes to rapidly here, for example. Especially noticeable when we’re parallel to the spline.