PSA: You Can Still Play One Game Across Two Switches, But Not Online Anymore
Or together via local multiplayer.
With the introduction of Virtual Game Cards, Switch owners can now conveniently swap digital games from one Switch console to another. However, it's been noted that players can no longer boot up the same game simultaneously across two Switch consoles while online.
The good news is that while you can no longer utilise the old method of using primary and secondary accounts and whatnot, there is a loophole that lets you boot up the same game on multiple systems. (More on that in a moment.)
Read the full article on nintendolife.com