Hi Dan!
Apparently there are two dialogues:
- One at the context menue of the layer: Data | Export Raster.
- And on the other one at "Share" and "Export map".
This offers your suggested option "32Bit with alpha".
No 2. works for adding to ArcGIS Pro, but unfortunately not for consuming into ArcGISRuntime.
I worked a little bit with the NoData symbology. But geotiff sepcification and NoData seems to be incomplete...
If I export the map to a TilePackage (tpk) - if works for ArcGISRuntime V100.8.
But for the requested workflow a single geotiff (or similar) is significantly better.
Any hints?