Remove sketched style of an image

[rich2005]

Try from the original scan

A small Gaussian blur: Filters -> Blur -> Gaussian Blur
Color -> Threshold
Filters -> Enhance -> Anti-alias

or using the gimp_gmic_qt plugin from http://www.gmic.eu (there is a Windows installer there)
Color -> Threshold
Gmic -> Testing -> PhotoComix -> PhotoComix Smoothing

Both of those as this quick animation https://i.imgur.com/Yh2xlC5.mp4