For the terrain size , i use now the best matching box

Technology content aware fill, which other assets use to remove shadows, is not quite suitable for this.
You will be happy if, together with the removal of shadows, you lose other objects from texture (eg, rivers, lakes, buildings, trees)?
And you will not just lose it, and some objects will be moved/copied to other random places.
I tested this feature in other assets, and every time I was surprised by the result.

Content aware fill is present in most serious graphic editors (such as GIMP or Photoshop).
If you need it, you can export the texture, use content aware fill, and import the texture again.
And it will work much better, because you can control the result.

Thank you for reporting that exported heightmaps flipped vertically.
We will fix this in the next version.

This asset is almost perfect, but there no shadow remover

Im actualy struggeling to select areas at a specific Width, ex 60km*60km

Also, export terrain fonction should flip the heightmap vertically.