The Pokémon Sword and Shield its launch was successful. A lot of players are jumping into the game and enjoying their experience in the Galar region. Unfortunately, the online service sometimes has a few hiccups from time to time, and some people know the message, "Online servers are under maintenance," an in-game message or something like that.
This can happen for a number of reasons, the most important of which is Nintendo servers - they handle certain background tasks and change each player's experience. Unfortunately, Nintendo does not go into the details of these outages and sometimes may not provide the full details.
However, they do have a dedicated webpage to provide Pokémon Sword and Shield players with useful information. If you go to this support page, there is a current status of The servers and you can indicate if there are The notable issues on the sites or if everything is okay.
There are two important sections of this web page. The first is the Online Service Status section. You can tell if the servers are down or having problems when you access the page. If you were attempting to access the game at an earlier date and encountered an issue, you can click the View Previous Info button to see if the issue was on your side or Nintendo's. They'll show the date and time of the reported outage, but they don't provide too many other details.
The second part, Maintenance Information, is useful for future dates. Nintendo will release its results as soon as any scheduled maintenance is scheduled. You will not receive a calendar one month in advance, but you can check this area to see any updates scheduled for release in the coming week. Below you can see click on View Completed Maintenance to learn more about previous service parts and their completion time. This check gives you a good idea of how long the online service is active. Sword and Shield will be down, based on past maintenance experiences.
Game Freak, and the game developers, unfortunately don't seem to provide too many complex details on these pages. If you're having trouble with the Pokémon Sword or Shields online service, these are great places to go to find out what might be going on when you want to play. Online service will be a bit difficult to follow after game maintenance, so expect a few hiccups on the same day of maintenance.