How to refine coastline of 1200+ islands' in Finnish archipelago?

I’d like to understand what is required to semiautomatically refine the coastline of over 1200 islands in the area of Nagu in the Finnish archipelago.

I can derive island coastline vector polygons from the National Land Survey of Finland’s material - see GeoPackage maasto here from which sea areas (“meri”) can be inverted to islands. The material is licensed CC 4.0 BY as described here.

I do not see that it is feasible to manually upload each island’s trace and manually draw it - especially if this same process is to be used for the rest of Finland’s archipelago’s thousands of islands.

What methods are there available to do this work semiautomatically? I’m thinking there must be a way to somehow automatically match existing OSM-shapes with an improved shape and then perhaps one by one approve a suggested improved island coastline. How could that be done?