Nintendo performs maintenance on its systems and software regularly. Here is the current schedule as of April 30th, 2023:
Games
- Splatoon, Mario Kart 8 (maintenance began March 2nd, 2023)
- We have identified vulnerabilities with online play for this network service and have begun temporary emergency maintenance. We expect an extended maintenance duration while we address these issues and have not determined when online play will resume. We sincerely apologize for this inconvenience and appreciate your understanding. (Error code: 106-0811)
Services
Note that the 3DS and Wii U eShops are now closed permanently. You can still redownload any titles you have purchased, but purchases are no longer possible. Nintendo has a support article here regarding this. To be clear, most online services are still functioning.
- Online Play (Switch, Wii U, 3DS) – May 8th, 2023 from 6p-10p Pacific/9p-1a Eastern
[Sources: Nintendo, Perfectly Nintendo]