I've written a little iOS app to sync the device's photos to object storage. Backends currently supported are Backblaze B2 and the S3 compatible providers. If you are interested, you can join the TestFlight below. Please provide feedback. It does NOT use rclone, I couldn't find any practical way to do that.
I think it is very hard or impossible to call external binaries on IOS - is that the case?
I do compile an rclone for IOS - you can find it here: https://beta.rclone.org/test/testbuilds-latest/rclone-ios-5.0-framework/Rclone.framework/Versions/A/
I've no idea whether it actually works though!