Hi Shaun,
In Pro 3.7, there is a new tool called Extract Scanned Lines that can achieve what you are aiming to do. The tool is designed to handle raster imagery created from scanned maps and diagrams. It detects linear features from the image and has options to indicate how wide the lines can be in pixel units and whether the line can have gaps, and how wide those gaps can be. The result is a centerline feature that constructs a smooth line and approximates curves and corners based on configurable tolerance values.
The tool requires the image to be a single band integer raster. The image from your screenshot could be reclassified to separate the darker dashed lines from the other lines so that the dashed lines can be uniquely extracted without being merged with the other linear features.
If you are interested in trying out the new tool, consider signing up for the ArcGIS Pro Early Adopter Community so that you can have access to Pro 3.7 Beta and let us know how the tool works for you. You can find out about when the beta is available here, which should be sometime in the next week or so:
https://link.esri.com/ProRoadmap
Regards,
Khalid
