FYI Just Dance 2019 servers are still supported, however there's an issue when the game attemtps to play online due to an issue with Nintendo Network. I've contacted Ubisoft support, and they said that they are aware of the issue and is currently investigating it.
Post
The error that appears when attemping to go online in the game is error code 102-2472. Which means that the games Client ID is Invalid. This should not happen normally. Other games are affected too. So Nintendo seems to have screw-up something on Nintendo Network.