you don’t need to export the raster as a tif file, you can open the img file in the data folder of your DIMAP product in any other GIS.
It differs how you define the no-data value in a GIS: S1 tile in QGIS: Zero values
If you post external materials, such as this map, please include the source. This not only good practice regarding copyright regulations but also gives others the chance to understand how it was created. Simply writing “I want a map like this” is quite challenging 