Won't let me join my little cousin to play with me on spitscreen for switch

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This is related to a different project. Use one of the links below to go to the correct project.
– Minecraft: Java Edition — Windows, Mac, and Linux
– Minecraft Launcher — bugs about the Minecraft Launcher specifically
– Minecraft: Bedrock Edition — Gear VR, iOS, Android, Windows 10 (from the Windows store), Xbox One, Windows 10 Mobile, Fire TV, Nintendo Switch, and PS4
– Minecraft: Earth — AR Compatible Devices

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