Nintendo has permanently banned some Switch 2 consoles from accessing online services due to the use of a microSD card-equipped flash cartridge called Mig. The ban affects users who have used the Mig to download and play pirated games or copies of games they own, rather than playing from their original cartridges.
The makers of the Mig cartridge have taken steps to distance themselves from piracy, but Nintendo still considers using the device to play pirated games as a violation of its user agreements. However, users with banned consoles can still unlink Virtual Game Cards from their accounts and load them onto other Switch devices.
Nintendo’s aggressive stance on piracy is not surprising, given its history of pursuing those who pirate its games and build emulators that can run pirated copies. The company has taken measures to ensure gamers play by its rules, particularly for its fastest-selling console, the Switch 2.
Source: https://www.theverge.com/news/688483/nintendo-switch-2-ban-error-code-mig-flash-cartridge-online