Nintendo announced that as of April 8, 2024, it will no longer support online services for the 3DS or the Wii U. This will include online co-op or multiplayer, internet rankings, and data distribution.
You will still be able to play offline games, and Pokemon Bank and Poke Transporter will still be available as well. Nintendo does note that support for Pokemon Bank and Poke Transporter may end in the future though. StreetPass will be available too, because it uses local communication between 3DS systems. However, you won’t be able to use SpotPass. Finally, it will be possible to download update date, as well as redownload games and DLC you own from the eShop.
Nintendo has been phasing out both the 3DS and the Wii U for a while now. The eShop for both consoles closed down in March 2023. Nintendo also announced that it would close down online services for the Nintendo 3DS and Wii U back in October 2023. This is not a surprise considering how old these consoles are. The 3DS first came out in 2011 and the Wii U launched in 2012.
You will no longer be able to access online services on the 3DS or the Wii U after April 8, 2024. However, you will still be able to access StreetPass, as well as download games and DLC you previously purchased.