First, some background info. In order to share the same digital titles on two Nintendo Switch systems, you’ll need to set your main Switch as the primary system and your second Switch as the secondary system. The secondary system must be connected to the Internet at all times in order to play the digital titles shared by the primary system.
So, in order to play the same game simultaneously, all you have to do is to disconnect the primary system from the Internet, so Nintendo can’t check whether your primary system is playing the same game. You can leave the secondary system online.
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