OP Updated for clarification -RavenXtra
The link is there, just slightly hidden:
The UK site does mention this, so I that's where this news comes from:
After my Nintendo Switch Online subscription expires, will my Save Data Cloud files and Nintendo Entertainment System – Nintendo Switch Online save data be erased?
Save data stored with Save Data Cloud cannot be kept outside of the duration of your Nintendo Switch Online membership. Nintendo Entertainment System – Nintendo Switch Online also uses the Save Data Cloud, so the same applies. However, if you keep the Nintendo Entertainment System – Nintendo Switch Online save data saved locally on your Nintendo Switch console, then you can use it again if you purchase another membership.
The US does give some additional info:
Is my save data retained if I cancel my Nintendo Switch Online membership?
We are unable to guarantee that cloud save data will be retained after an extended period of time from when your membership is ended. However, you can continue to use the save data that is saved to your system memory.