Nintendo Switch System Update Information v20.0.0 | Nintendo Support

This afternoon, a friend brings its Switch with Mario Kart (she have the DLC on this Switch and another Switch at home) and had some message about update and shared DLC.

We actually could not play the DLC because the second Switch on its home was not uptodate and online.

Dunno what it means, but I suspect you could have some surprise if you have no access to your other Switch.