Journelly uses standard iOS file access and relies on iCloud (or third parties) to handle syncing via related infrastructure.

Theoretially, any third party app that is a file provider https://developer.apple.com/documentation/fileprovider should be able available to Journelly.

The reality is that reliability and provider completeness by third parties varies drastially. For example, many of them don't offer directory access to other apps (Nextcloud as an example https://github.com/nextcloud/ios/issues/3283#issuecomment-27...), which is a show-stopper for Journelly. It needs a directory to save images.

Here's a thread with some third party options some folks are using with Journelly https://framapiaf.org/@marczz/114369575100101184

Working Copy, SyncTrain, and Möbius Sync are amongst the ones I've heard working from users. For v1, I'm officially supporting iCloud (but still leaving it open for folks to try other providers). I'm just not able to do what's necessary to implement or fix what's needed in those providers (their app/codebase).