Unfortunately it has been discovered that not all games support cloud save, as reported by Game Informer who discovered several Switch games, such as Pokémon Let’s Go Eevee & Pikachu and Splatoon 2, do not support the feature. It reads, “Nintendo Switch Online membership (sold separately) and Nintendo Account required for online play. This game does not support Save Data Cloud backup. Not available in all countries. Internet access required for online features.”
Nintendo has since responded to the publication and clarified why not all games support the feature, which they cite reasons such as item trading and “fairness” in online play as being some of the reasons. “The vast majority of Nintendo Switch games will support Save Data Cloud backup. However, in certain games this feature would make it possible to, for example, regain items that had been traded to other players, or revert to a higher online multiplayer ranking that had been lost.”
“To ensure fair play, Save Data Cloud backup may not be enabled for such games. To ensure that Save Data Cloud backups cannot be used to unfairly affect online multiplayer rankings, the feature will not be enabled in Splatoon 2.” We suppose that makes sense, although whether or not this will appease gamers remains to be seen.