In case you missed it, Nintendo recently updated its official game page for Splatoon 3 - revealing the third entry will support cloud saves. The catch is it seems cloud saves will only be compatible with offline play data.
Here's the full footnote from Nintendo's game page, which also mentions how membership is required to access additional features online features:
Save Data Cloud compatible with offline play data only.
Nintendo Switch Online membership (sold separately) and Nintendo Account required for online features. Not available in all countries. Internet access required for online features. Terms apply. nintendo.com/switch-online
It's worth noting Splatoon 2 did not include cloud save support, and while Splatoon 3 won't include additional cloud support for the game's online features this is at least a step in the right direction.
At this stage, it's still unknown how exactly data will be saved for the online components of Splatoon 3.
If we hear anything else on this subject, we'll let you know.