Does disabling chat for everyone effect external meeting also?

If I disable chat for the enterprise, does it also disable chat in external meetings?

That would not be good.

What are my options to make external still work, but not in same domain

Disable Chat offers the below options:

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Allow users to chat with others
If you select 'In the same organization', users may still be able to chat with external users if they are added to channels or group chats with external users.

Anyone (internal and external contacts)

In the same organization

In the same organization and specified domains

In the same organization and specified users