Update: The new patch notes say that they have “added Dark Mode” but it seems to have added a “Light Mode”.
The Nintendo Switch Online application has been updated today and it has finally added the option to view it in Dark Mode. It’s been a long time coming since the Nintendo Switch Online smartphone application has been available since 2017. To change the app to the newly added Dark Mode you simply need to go into the app’s settings. If you are on iOS, Dark Mode only works on iOS 13 onwards but we are already on iOS 15, so it shouldn’t be too much of a problem for the majority of users.