I had a look into this & tried it in a couple of areas. While it works wells enough in principle once you’ve got a heightmap downloaded for an area it seems to be only as good as the OSM source. In the SDK you end up with terraforming polygons placed correctly around every body of water in an area except for the ones causing these spikes. You might catch some of the spikes but you get loads of polygons you don’t need because most of the water is ok. Then you still have to go through & manually scan an area for the one’s that aren’t on OSM.
It is a nifty little qgis modeller Henrikx made though.