First I tried your example with "SchematicPolygon". Use separate cells for each of the following commands, if possible. I am showing the output of the last command.
region = EntityValue[Entity["Country", "SouthKorea"],
"SchematicPolygon"] /. g_GeoPosition :> g["LongitudeLatitude"]
newregion = RegionResize[region, 10]
Then I switched various other countries and notebook wouldn't evaluate properly and plot two different countries one on top of the other, unable to reassign
region. Evaluation->Quit Kernel->Local was grayed out. So I terminated Mma and restarted.
This time I used yet another country, and it remembered the last country. (persistence).
Then I tried "SouthKorea" but this time with "Polygon". The image below shows that it can be done.
Obviously, this is strange behavior. I am on Mma 12.2 Win7-x64 8GB. It takes less than 5 seconds to do these calculations.