Can you play 2 different islands on one device(etc. Nintendo) in animal crossing?

You can only create one island per Nintendo Switch system, even if you use multiple games. A different system is required to create a different island. The island save data is saved on the Nintendo Switch system, so there will only be one island (save file), even if different games are used on the same system.

Explanation:

No, you can NOT have multiple islands in Animal Crossing: New Horizons. Each Nintendo Switch system is limited to just ONE island. ... The only way to access multiple islands is by having friends with their own Animal Crossing: New Horizons island to visit.

Explanation:

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