Nintendo Japan and Nintendo of Europe announced today the date that the Nintendo 3DS and Nintendo Wii U eShop will stop allowing people to purchase games in those stores.
Furthermore, Nintendo announced that the function to add money to the Nintendo 3DS and Nintendo Wii U eShops from prepaid cards will stop on August 29, 2022, though if loaded up before that day, the funds can be used until March 27.
Even after 27/03/2023 and for the foreseeable future, it will still be possible to redownload games and DLC, receive software updates and enjoy online play on Wii U consoles and Nintendo 3DS systems.