Minecraft beta can't join cossplatform in to Minecraft preview

Hello, Henry. I'm Arturo, a community user like you, and I'll be glad to provide assistance with your inquiry today.

I’m sorry to hear you are having trouble with Minecraft.
Not only that, but I want to inform you that if Minecraft is the only game affected, it is suggested to report the problem to their dedicated support team.

They will be able to provide further assistance if needed, and you can do it below:
https://help.minecraft.net/hc/requests/new

Additionally, it is important to mention that even if Microsoft owns Minecraft/Mojang, they remain as a separate company, including the assistance for specific game issues.

However, as a general recommendation, you may want to check if the issue persists on the regular Minecraft edition as well, or after connecting the affected device to a different Wi-Fi network, like a mobile hotspot.

Thanks for reading me and for your kindness.

Regards,

Arturo.

Your friend may indeed have a beta version of Minecraft. If that is the case, they will not have access to Realms and will not be able to join non-beta players while previewing the beta.

According to what's mentioned in the link below (section: Essential information before participating in a Minecraft Beta), you can't switch back and forth between the two programs. You can find more information about this in the following link :

How to Join (and leave) a Minecraft Beta – Home

Is it possible that one of you or your friends has joined the Minecraft Beta Insider program?

If so, you probably have different versions of the game, and only players with the same Minecraft version can join each other's worlds.

Check that you all have either the official Minecraft version of 1.11.4. If one (or more) have the current Beta version of 1.13.something, then you can't join each other's worlds.

I recently joined the Beta version of Minecraft on my Xbox one. when I left the preview, I reinstalled Minecraft. But when I launch Minecraft, It automatically installs the beta. Even when I cancelled the update, when I launch the game, It updates. I even tried closing my Insider hub account for this to stop but it didn't. Any help please?

You must leave the beta club thing, and re-install Minecraft. I hope i helped