I believe the "bonus digital content" is referring to the Zenith starship and the Shredder weapon, which can be played if you select digital play rather than using the toys.
For two players you need two sets of controllers connected to the same Switch console. The Switch console needs to be docked, in TV mode, so the Switch Lite can't do two-player. You may need to go out to the Switch main screen and pull up the Controllers menu to get the second set of controllers connected. If I recall correctly, you press the + button on the second controller when the game is running to request to be added in as a second player.
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