As of late March 2023, it will no longer be possible to make Nintendo eShop purchases for the Wii U and the Nintendo 3DS family of systems. They're not shutting down, you'll just be unable to purchase anything else.

Also, as of May 23, 2022, it will no longer be possible to use a credit card to add funds to an account in Nintendo eShop on Wii U or the Nintendo 3DS family of systems. And as of August 29, 2022, it will no longer be possible to use a Nintendo eShop Card to add funds to an account in Nintendo eShop on Wii U or the Nintendo 3DS family of systems.
(However, it will still be possible to redeem download codes until late March 2023.)

Dammit Nintendo. What does this mean for Pokémon Bank, I wonder?


EDIT:
From Serebii:

Today, Nintendo announced that the Nintendo 3DS and Wii U will close their eShop at the end of March 2023. With this, The Pokémon Company has announced that Pokémon Bank will be free to use when that happens, though new downloads of Pokémon Bank will no longer be possible. There is presently no end date for the free service

Well, that's something at least.