I am trying to download my save backup from the cloud onto the Nintendo Switch.  However, when I go to the Save Data Cloud tab, it says "This software does not support backup via the Save Data Cloud Service".

I tried uninstalling/re-installing the game, and nothing changed.  I also did a factory reset of the console and after re-installing the game, it showed me that there was indeed a cloud backup available.  However, when I tried to download the save, the download wouldn't initialize and I'm back to seeing the above message.

Not sure if this feature was removed, if it's a problem on your side, or if it's Nintendo's problem.  However, after searching Reddit and other forums, there appear to be multiple people affected by this.