The online servers for Wii U and 3DS systems will end support at 4 p.m. Pacific time and 7 p.m. Eastern time as announced by Nintendo back in late 2023. Obviously you won't be able to access the eShop to redownload digital games that you owned on your account, lobbies will be inaccessible and Spotpass features from 3DS systems won't be available.
Regardless of the flop that the Wii U was, I still enjoyed playing the games on mine, and I loved playing with friends on the 3DS,