Hi @laurammg

You should be able to write to ArcGIS online using the Esri ArcGIS Online (AGOL) Feature Service Writer however from the Quick Facts page of that help documentation it doesn't look like raster geometry is supported at this time.

Here are some other resources that might help you get started using our AGOL writer though:

FAQs for ArcGIS Online: https://knowledge.safe.com/articles/24871/quick-tips-for-arcgis-online-frequently-asked-ques.html

Update an existing ArcGIS Online Service: https://knowledge.safe.com/articles/19302/how-do-i-write-updates-to-an-existing-arcgis-onlin.html

Bring CAD data into ArcGIS Online (plus other data formats): https://www.youtube.com/watch?v=XivCpR7vTDw

Is this possible on the latest FME build?

Sorry, not that I can see: https://docs.safe.com/fme/html/FME_Desktop_Documentation/FME_ReadersWriters/arcgisonlinefeatures/quick_facts_arcgisonlinefeatures.htm