When you get a second console you have to designate one as your primary console and one as your secondary console. Register your switch account to the new console and download the games you want on that second console. Your primary console you can play your games whenever. For your secondary console, it will check your switch account on your primary console to make sure the game is not currently being run. So you'll need to make sure it's connected to the internet. This can be a little obnoxious if, say, you're in a car traveling and don't have it connected to wifi. You may need to connect to a mobile tethering hotspot in such a case.

So you can't play the digital game at the same time on multiple consoles, but each console can play the digital game separately.