Amazon / Google... Google / Amazon ... we decided to take the plunge and go for Google Cloud services as their services seem to be a bit more thought through and structured as they have not developed so organically.
Uploaded file storage from the app
Cirrus CI can store build artifacts in Google Cloud Storage
Flutter iOS App
We use Google Cloud Storage to store the images and other files that are added (uploaded) or generated in the Flutter application.
All comments, votes, and other actions live here as a highly-scalable, reliable, multi-region storage solution.